FR2842601A1 - Mechanically-valved spark plug probe measuring fuel concentration of mixture in engine cylinder, includes resistors sensing pressure, velocity and temperature - Google Patents

Abstract

A sensitive section (51C) of the third resistor (50C) is located in the mixture passage. It is connected to a supply (55C) controlled to maintain the resistance value constant. The sensitive sections (51A-C) of the three resistors are located in a fluid passage, such that pressure, velocity and temperature of the fluid are sensibly uniform at this location. An independent claim is included for the corresponding method of measuring the fuel concentration in the mixture.

Description

The present invention relates to a probe for measuring the concentration of

  fuel from a fuel mixture, which

  uses the principle of the so-called "hot wire" anemometer.

  So-called "hot wire" anemometers are well known in the art. They include a resistive wire placed in an air flow, this wire constituting a branch of a Wheatstone bridge and being electrically powered. The resistive wire, whose resistance value is variable with its temperature according to a known law, is kept at a constant temperature

  corresponding to the balancing of the Wheatstone bridge.

  The wire being swept and cooled by the air current, all the more that the air flow is important, it is understood that the electric power to be supplied to the resistive wire to maintain it at constant temperature, electric power dissipated by Joule effect in the resistive wire, is all the more important as the air flow is important. Solving the heat balance equation at wire level provides access from electrical power

  supplied, at the speed of flow.

  Also known in the prior art, sensors for measuring the fuel concentration of a fuel mixture, comprising a mixture inlet and outlet defining between them a mixture passage, a first resistive electrical conductor including a sensitive section is adapted to catalyze an oxidation reaction of the fuel and disposed in the mixture passage, a second resistive electrical conductor of which a sensitive section is disposed in the mixture passage, each conductor being able to be electrically connected to a respective suitable supply device for electrically supplying said conductor so as to maintain its

constant resistance.

  A probe of this type is for example described in the

document FR 2 757 213.

  Such probes are implemented so as to produce a catalysis on the first wire (designating the sensitive part of the first conductor), while the second wire does not produce catalysis. For this, either the second wire is made of a non-catalytic material, or it is brought to a temperature below the trigger (or priming) threshold temperature of

catalysis.

  The fuel concentration is calculated by solving the two heat balance (or calorific) equations corresponding to the two wires respectively. The first equation, which corresponds to the first wire, shows a term of catalytic thermal power, function of the concentration of the fuel mixture. By neglecting the term power d at radiation, the heat balance equation respectively at the level of the first and the second wire, is expressed by the relation: (i) Pjoule + Pcatalytique = Pconvexion + Pconduction, (ii) Pjoule = Pconvexion + Pconduction O Pjoule represents the calorific intake of food

electric.

  However, these equations involve a number of parameters greater than the number of equations. In order to be able to solve these equations, in which the concentration of the fuel mixture and the speed of the fluid in the vicinity of the wire are unknown, parameters such as the pressure of the flow at

  wire level, and flow temperature.

  For this, certain current probes are designed to bring the flow to atmospheric pressure at the level of the wires, and to pass the mixture through a heated passage upstream of the sensitive wires, so as to

  bring the mixture to a known and controlled temperature.

  The provisions aiming at eliminating the term of flow temperature imposes a long journey between the sampling point and the measuring point. The response time of the probe, that is to say the time difference between the measured value and the actual value, is lengthened in a penalizing manner. In addition, the measurement is marred by a relatively large error, the probe has a great complexity of design and

  manufacturing, and its size is important.

  The object of the invention is to resolve these drawbacks, in particular to propose a probe making it possible to bring the measurement point closer to the sampling point, so as to reduce the reaction time (to bring it to around 200 ps / tenth of wealth unit), in

  also improving the accuracy of the measurement.

  To this end, a measurement probe according to the invention comprises a third resistive electrical conductor, a sensitive section of which is arranged in the mixing passage, said third conductor being able to be electrically connected to a supply device suitable for electrically supplying said third. electrical conductor so as to maintain its constant resistance, and the sensitive sections of the three conductors are arranged in a region of the fluid passage such as the pressure, speed, and temperature conditions of the

  fluid are substantially uniform.

  According to other characteristics of the invention - the sensitive section of the first conductor is a wire made of an alloy of platinum and iridium, in particular of a composition of 80% platinum and 20% iridium; - the sensitive sections of the three electrical conductors are made of the same material; - The sensitive section of each conductor has a diameter between 15 and 25 µm; - the passage has a neck of calibrated dimension - the sensitive sections of the conductors are arranged downstream of the neck; the probe comprises a body in which the mixing passage is arranged and in which the electrical conductors are arranged, the probe further comprising a spark plug adapted to be connected to an ignition control device, the electrodes of the spark plug protruding from the body on the entry side of the passage, and the body having an external geometry such that the probe can be mounted in the orifice of a combustion chamber of an internal combustion engine, in particular of a motor vehicle , designed to receive a spark plug; - The probe includes a pressure sensor disposed in the body on the side of the passage entrance; and the probe comprises a sampling valve which can be connected to a valve control device, and arranged so as to selectively open or close the entry of the passage according to a set point of the

valve control device.

  The invention also relates to a device for measuring the fuel concentration of a fuel mixture, comprising a probe as described above, and a respective supply device for each conductor, adapted to supply the respective conductor electrically so as to maintain its constant resistance over a measurement time interval. This device is characterized in that the electrical supply devices operate in such a way that the respective values of operating resistance of the electrical conductors

are all different.

  According to other characteristics of the device according to the invention: the operating resistance of the first electrical conductor corresponds to a temperature of the respective sensitive section greater than or equal to a temperature for initiating catalysis; - The operating resistances of the second and third electrical conductors correspond to temperatures of the respective sensitive parts lower than the catalyst initiation temperature; the device comprises means for measuring a significant electric quantity of the electric power supplied by each supply device to the respective electric conductor, and calculation means suitable for calculating the fuel concentration of the mixture from said electric quantities; the measurement means comprise synchronization means generating a time base for the operation of the measurement device; the device comprises an ignition control device connected to the spark plug, the ignition control device and the conductor supply devices being connected to the synchronization means so that the calculated fuel concentrations can be correlated with the spark plug ignition cycles - the device comprises a module for processing the signal from the pressure sensor, said processing module and the devices for supplying the conductors being connected to the synchronization means, so that the calculated fuel concentrations can be correlated with the measured pressure values; the device comprises a camshaft rotation sensor, said sensor and the devices for supplying the conductors being connected to the synchronization means, so that the calculated fuel concentrations can be correlated with the points of the engine cycle; and the measurement means comprise data acquisition means receiving as input the measured data and the time base from the means of

synchronization.

  Finally, the invention relates to a method for measuring the fuel concentration of a fuel mixture, in which: - a quantity of mixture is taken - this quantity of mixture is passed under substantially uniform conditions of temperature, pressure and speed , on three sensitive sections of three respective electrically supplied conductors, said sensitive sections being brought to three different constant temperatures over a measurement time interval, a first of the three sensitive sections being adapted to catalyze an oxidation reaction of the fuel; - we calculate, from significant electrical quantities, the power supplies of the three

  conductors, the fuel concentration of the mixture.

  According to other characteristics of the process according to the invention: - the three sensitive sections are made of an identical material, and in which the first sensitive section is maintained at a temperature greater than or equal to a temperature for triggering catalysis, while the second and third sensitive sections are maintained at temperatures below said catalysis initiation temperature; and - the mixture is sampled or prohibited selectively, as a function of significant parameters of thermodynamic conditions of the mixture. An embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a measuring device according to the invention; and - Figure 2 is a partial sectional view of a

probe according to the invention.

  In Figure 1, a probe 1 of

  fuel concentration measurement according to the invention.

  This probe has been shown mounted on a cylinder 3 of a combustion engine, for example of a motor vehicle, in place of a spark plug. The probe 1 is designed to take an amount of fuel mixture in the combustion chamber 5 of the cylinder 3, through a mixture inlet 7, to conduct this amount of mixture to a sensitive part 9 of the probe, and to evacuate this amount of mix towards an outlet there, which is an orifice

in the open air.

  In what follows, we will define "the front" of the probe as the part of it located on the side of the inlet 7, while we will define "the rear" as the part

located on the opposite side.

  In the example illustrated in the Figures, the probe also includes a spark plug 13, the electrodes 15 of which, in operation, project from the side of the inlet 7 inside the combustion chamber 5. The spark plug 13 is associated with an ignition control device 17 capable of controlling the operation of the spark plug in synchronization with the other spark plugs of the engine. Thus, it is possible to carry out a measurement of the fuel concentration in the combustion chamber 5, by means of the probe 1, without disturbing

  important way the engine works.

  The probe 1 further comprises a pressure sensor 23, associated with a module 25 for processing the signal from said sensor, and provided for measuring the pressure prevailing in the combustion chamber 5. Thus, the probe makes it possible to correlate the concentration measurement in fuel with the measurement of another quantity, in this case the pressure,

  significant from the point of the engine cycle.

  Referring now to Figures 1 and 2, we will describe in more detail the structure and operation of

  probe 1 and the associated measuring device.

  The probe 1 comprises a probe body 31 of which a section 32 situated on the side of the mixing inlet 7 has an external geometry, such that the probe can be mounted in the orifice of the combustion chamber 5 intended to receive a candle ignition. Section 32 can be threaded so that the probe 1 can be screwed onto the cylinder 3, in the manner and in place of the spark plug

  mounted for normal engine operation.

  The probe 1 comprises a sampling valve 35 capable of blocking or releasing the mixing inlet 7 as a function of a control signal emitted by an associated valve control device 37. The valve 35 has a valve stem 41 sliding in the body 31, and a head of

  valve 42 capable of blocking or releasing the inlet 7.

  In the body 31, a fluid passage 45 is formed connecting the inlet 7 to the outlet 11. The passage 45 has a neck 47 of calibrated dimension, making it possible to control the

  fuel mixture flow flowing in the probe.

  The sensitive part 9 of the probe 1 comprises three electrical conductors 50A, 50B, 50C, of which a respective resistive sensitive section (or wire) 51A, 51B, 51C extends in the passage of the mixture (or fluid), transversely to

  the direction F of fluid flow.

  Preferably, as shown in the Figures, the sensitive sections 51A, 51B, 51C are placed downstream of the neck 47, in a region close to the outlet 11, so that the fluid is, in this region, under substantially uniform conditions pressure (in this case the

  atmospheric pressure), temperature, and speed.

  Also thanks to this arrangement, we ensure a better

thermal protection of the wire.

  Each conductor 50A, 50B, 50C is supplied by a respective power supply device 55A, 55B, 55C which comprises an electrical power source associated with a Wheatstone bridge (not shown), of which the respective conductor SOA, 50B, 50C constitutes one of the branches. The supply device 55A, 55B, 55C is designed to maintain the Wheatstone bridge in its state of equilibrium which corresponds to a constant resistance of the conductor 50A, B, SOC, i.e. a constant resistance of the sensitive section 51A, 51B, 51C. Since the resistance of the sensitive section is a known function of the temperature of the sensitive section 51A, 51B, 51C, the supply device A, 55B, 55C is adapted to keep the temperature of each sensitive section or wire constant, at a value

known.

  Each supply device 55A, 55B, 55C is

  connected to calculation means 61 via measurement means 62.

  We have seen that the measuring device which is the subject of the invention comprises a certain number of sensitive members assembled in the probe 1, these members being here made up of part 9 and of the pressure sensor 23, and the valve 35. It has been seen that the measuring device also comprises the supply devices 55A, B, 55C, the module 25, and the valve control device 37. The spark plug 13 integrated in the probe 1 and its control device 17 are also part of the measurement device. In addition, one can provide in the measuring device, as shown in Figure 1, a camshaft rotation sensor 61 which can accurately determine the angular position of the camshaft, and therefore the cycle point motor at all times t

of measurement.

  The measurement means 62, which are associated with the calculation means 61, complete with them the measurement device. These measurement means 62 include means for

  synchronization 67 and acquisition means 69.

  The operating principle of probe 1 is based on the principle of the "hot wire" anemometer as described in the preamble to the application, one of the three wires being moreover capable of catalyzing an oxidation reaction.

fuel.

  For this, the three wires are made from the same alloy of platinum and iridium, for example composed of 80% platinum and 20% iridium, but only the first wire 51A being brought to a temperature sufficient to carry out the catalysis. . More specifically, the first wire 51A is electrically supplied by its supply device 55A so as to achieve, over a measurement interval, the equilibrium of the associated Wheatstone bridge for a fixed wire temperature, greater than the threshold temperature. triggering of catalysis. For the alloy composition which has just been given, the catalyst initiation temperature for a fuel in common use in internal combustion engines of a motor vehicle can be approximately at 700 K. The operating temperature of the first 51A wire can

  then be chosen to be substantially equal to 950 K + 5%.

  If the two other wires 51B, 51C are, as is the case in the example described, made of the same alloy as the first wire 51A, their operating temperatures must be strictly lower than the catalytic threshold temperature. In addition, the temperatures of the second 51B and third 51C wires must be different from each other. For example, they can be chosen substantially

  equal to 650 K + 5% and 450 K + 5% respectively.

  Alternatively, the second and third wires could be made of tungsten and operate at any two temperatures, different from each other, the tungsten not being a catalyst for the reaction

fuel oxidation.

  In order to have a short response time, the wires must be of small section. For example, they can have a diameter of between 15 and 25 μm, a range which resolves with a good compromise the aforementioned problem and the problem of using the wires, in particular determined by

the difficulty of soldering them.

  As explained in the introduction to the request, the electrical power supplied to each of the sensitive wires 51B, 51C corresponds to a power dissipated by the Joule effect (convective exchanges) to maintain the wires at their

respective temperatures.

  The values VA, VB, Vc of the electric power supplied by each of the supply devices to its respective wire are supplied to the measurement means 62, which communicate with the ignition control device 17, the signal processing module 25 pressure, the valve control device 27, and the rotation sensor 65. Thus, the power values VA, VB, Vc of the power supplied to the respective sensitive wire 51A, 51B, 51C are, thanks to the time base supplied to the entire device by the synchronization means 67, correlated with one or more of the ignition control, pressure inside the combustion chamber, valve position, or angular position of the camshaft. All these data are significant from the point of

  engine operating cycle at the time of measurement.

  In particular, the point of the ignition cycle given by the ignition control device 17 is significant of the point of the engine cycle. In addition, the state of the bleed valve 35 determined by the valve control device 37 is indirectly linked to the point of the engine cycle, since the device 37 controls the opening or closing of the valve 35 depending on the point reached in the engine cycle. Thus, for example, the valve 35 is ordered to close immediately after combustion of the mixture contained in the chamber 5, in order to avoid deterioration of the conductor 50A, 50B, 50C, in particular of the sensitive section 51A, 51E, 51C , by too much heating. The point of the engine cycle is therefore associated with significant parameters of thermodynamic conditions of the mixture, according to which one authorizes or prohibits

mixing sample.

  The acquisition means 69, which are connected to the synchronization means 37, receive as input the values VA, VB, Vc transmitted to the measurement means 62 via the synchronization means 37, and the time base provided by the synchronization means 67. The acquisition means 69 store these data and direct them to the calculation means 60 in the form of measurement signals SA, SB, SC. The calculation means 61 solve the energy balance equations expressed in the form (i) at the level of the first wire 51A, and in the form (ii) for the other two wires 51B, 51C, to deduce therefrom

  fuel concentration of the mixture sampled by the probe.

Claims (21)

REVENDI CATI ONS   1. A probe for measuring the fuel concentration of a fuel mixture, comprising an inlet (7) and an outlet (11) for mixing defining between them a passage (45) for mixing, a first resistive electrical conductor (50A), one sensitive section (51A) is adapted to catalyze an oxidation reaction of the fuel and arranged in the mixing passage, a second resistive electrical conductor (50E) of which a sensitive section (51B) is arranged in the mixing passage, each conductor ( 50A, 50B) capable of being electrically connected to a respective supply device (55A, 55B) adapted to supply said conductor electrically so as to maintain its constant resistance, characterized in that it comprises a third resistive electrical conductor (50C) of which a sensitive section (51C) is arranged in the mixing passage, said third conductor (50C) being able to be electrically connected to a supply device (55C) adapted to electrically supply said third electrical conductor so as to maintain its constant resistance, and in that the sensitive sections (51A, 51B, 51C) of the three conductors are arranged in a region of the fluid passage such as the pressure conditions, speed, and   fluid temperature are substantially uniform.   2. Probe according to claim 1, characterized in that the sensitive section (51A) of the first conductor (50A) is a wire made of an alloy of platinum and iridium, in particular of a composition of 80% platinum and 20 % iridium. 3. Probe according to claim 1 or 2, characterized in that the sensitive sections (51A, 51B, 51C) of the three electrical conductors are made in the same material.   4. Probe according to any one of the claims   1 to 3, characterized in that the sensitive section (51A, 51B, 51C) of each conductor has a diameter between 15 and / im.   5. Probe according to any one of the claims   1 to 4, characterized in that the passage (45) has a collar (47) of calibrated dimension.   6. Probe according to claim 5, characterized in that the sensitive sections (51A, 51B, 51C) of the   conductors are arranged downstream of the neck (47).   7. Probe according to any one of the claims   1 to 6, characterized in that it comprises a body (31) in which the mixing passage (45) is formed and in which the electrical conductors (50A, 50B, 50C) are arranged, the probe (1) comprising in addition to a spark plug (13) adapted to be connected to an ignition control device (17), the electrodes (15) of the spark plug protruding from the body (31) on the inlet side (7) of the passage (45), and the body (31) having an external geometry such that the probe (1) can be mounted in the orifice of a combustion chamber (5) of an internal combustion engine, in particular of a motor vehicle , planned   to receive a spark plug.   8. Probe according to claim 7, characterized in that it comprises a pressure sensor (23) arranged in   the body (31) on the inlet side (7) of the passage (45).   9. Probe according to any one of claims   1 to 8, characterized in that it comprises a sampling valve (35) which can be connected to a valve control device (37), and arranged so as to selectively open or close the inlet (7) of the passage (45) according to a setpoint of the valve control device (37). 10. Device for measuring the fuel concentration of a fuel mixture, comprising a probe according to   any one of claims 1 to 9, and a device   respective supply (55A, 55B, 55C) for each conductor (50A, 50B, SOC), adapted to electrically supply the respective conductor so as to maintain its constant resistance over a measurement time interval, characterized in that the devices power supply (55A, 55B, 55C) operate so that the respective operating resistance values of the electrical conductors (50A, 50B, 50C) are all different. 11. Device according to claim 10, characterized in that the operating resistance of the first electrical conductor (50A) corresponds to a temperature of the respective sensitive section (51A) greater than or equal to a catalyst initiation temperature. 12. Device according to claim 11, characterized in that the operating resistances of the second and third electrical conductors (50B, 50C) correspond to temperatures of the respective sensitive parts (51B, 51C) lower than the temperature initiation of catalysis.   13. Device according to any one of   claims 10 to 12, characterized in that it comprises   means (62) for measuring an electrical quantity (VA, VB, Vc) significant of the electrical power supplied by each supply device (55A, 55B, 55C) to the respective electrical conductor (50A, 50B, 50C), and calculation means (61) adapted to calculate the fuel concentration of the mixture from said electrical quantities. 14. Device according to claim 13, characterized in that the measuring means (62) comprise synchronization means (67) generating a base of   time for operation of the measuring device.   15. Device according to claim 14, wherein the probe conforms to claim 7, characterized in that it comprises an ignition control device (17) connected to the spark plug (13), the control device ignition (17) and the feeders of the conductors (55A, 55B, 55C) being connected to the synchronization means (67) so that the calculated fuel concentrations can be correlated with the cycles for igniting the spark plug (13).   16. Device according to claim 14 or 15, in which the probe conforms to claim 8, characterized in that it comprises a module (25) for processing the signal from the pressure sensor (23), said processing module (25) and the feeders for the conductors (55A, 55B, 55C) being connected to the synchronization means (67), so that the calculated fuel concentrations can be correlated with the values pressure measured.   17. Device according to any one of   Claims 14 to 16, characterized in that it comprises a   camshaft rotation sensor (65), said sensor (65) and the feeders of the conductors (55A, 55B, C) being connected to the synchronization means (67), so that the calculated fuel concentrations can   be correlated with points in the engine cycle.   18. Device according to any one of   claims 14 to 17, characterized in that the means for   measurement (62) include data acquisition means (69) receiving as input the measured data and the database   time from the synchronization means (67).   19. Method for measuring the fuel concentration of a fuel mixture, in which: - a quantity of mixture is taken; - This quantity of mixture is passed, under substantially uniform conditions of temperature, pressure and speed, over three sensitive sections (51A, 51B, 51C) of three respective conductors (50A, 50B, 50C) electrically supplied, said sections sensitive being brought to three different constant temperatures over a measurement time interval, a first (51A) of the three sensitive sections being adapted to catalyze a fuel oxidation reaction; - the electrical concentration (VA, VB, Vc) significant of the supply powers of the three conductors (50A, 50B, SOC) is calculated, fuel of the mixture.   20. The method of claim 19, wherein the three sensitive sections (51A, 51B, 51C) are made of an identical material, and wherein the first sensitive section (51A) is maintained at a temperature greater than or equal to a temperature of triggering of catalysis, while maintaining the second (51B) and third (51C) sensitive sections at temperatures below said   catalyst initiation temperature.   21. The method of claim 19 or 20, wherein the mixing sample is taken or prohibited selectively, according to significant parameters   thermodynamic conditions of the mixture.