FR2473720A1 - ELECTROCHEMICAL MEASUREMENT PROBE WITH PROTECTIVE DEVICE FOR DETERMINING OXYGEN CONTENT OF EXHAUST GASES - Google Patents

Abstract

The present invention relates to electrochemical measurement probes for determining the oxygen content of exhaust gases. The measuring probe comprises at its part exposed to the exhaust gases, a protection device 12 made of porous sintered material which surrounds it, thus only part of the flow of the exhaust gases and no longer their tone reaches through the pores to the measurement probe, which makes it possible to greatly attenuate thermal shocks and pressure peaks at the level of the solid electrolyte tube 1 of the probe. The protection device is advantageously placed at a distance of 0.01 to 20.0 mm from the measurement probe. The porous sintered material can be ceramic or metal, such as high temperature resistant nickel alloys. Application to the determination of the oxygen content of the exhaust gases of internal combustion engines. (CF DRAWING IN BOPI)

Description

2473? 20

-1-

  The invention relates to a measuring probe

  electrochemical reactor for determining the oxygen content of the exhaust gases, in particular from internal combustion engines, the part of which is exposed to the exhaust gases is surrounded by a protective device arranged around and at a certain distance from

  the measuring probe and having openings.

  Measuring probes for deter-

  the oxygen concentration in the exhaust gas

  of an internal combustion engine with a view to

  regulation of the air-fuel ratio of the fueling mixture

  this engine are known (patent applications in the Republic of

  Federal Republic of Germany DE-OS 24 33 158, DE-OS 25 02

  409, DE-OS 26 39 097, DE-AS 26 57 437, application for patent

  in the United States of America US-PS 37 59 232, or

  tomotive Engineering 87 (3), pages 88 to 97 of March

1979).

  These oxygen measurement probes often have a solid electrolyte (conductive

  of oxygen ions) in the form of a tube. On the inside

  re, exposed to the standard gas, solid electrolyte and on the outer face exposed to the exhaust gas, a platinum electrode (thin film electrode)

  consists of thermal vaporisation, spraying

  cathodic application, gas phase application, reduction

  In this case, the electromotive force thus created between these faces and which can be measured corresponds to the difference in oxygen concentrations or partial pressures.

  exhaust gas and standard gas. These probes can

  may also be manufactured from a compound of

  ceramic tane (Ti 02), most often impregnated with a precious metal, the electrical resistance of which varies with the oxygen content of the gaseous fluid and with the temperature. To increase the durability of such a measuring probe, the part of the probe that is exposed to the exhaust gas is surrounded by a protective device.

  On electrochemical measuring probes

  known, the part of the probe exposed to gases

  exhaust system is equipped with a bushing

  positive protection and having a number of openings (Patent applications in the Federal Republic of Germany DE-OS 23 15 444, DE-OS 26 29 097 or DE-OS

  26 27 760); the catalyst layer of the outer face

  of the probe, however, is quickly destroyed by the flow of exhaust gas

  and striking directly (including with large

  particles it contains) the catalyst layer. By

  elsewhere, the area of the probe behind the openings

  the protective device is not protected,

  as well as its catalyst layer, international shocks

  coming when occur in the incoming flow of

  exhaust gas from sudden changes in temperature

re and pressure.

  We also know devices for

  tubular protection and closed at one end, pre-

  several openings on their enve-

  lopped and equipped with baffle elements to prevent incoming gas from directly impacting

  on the solid electrolyte tube. On these forms of

  the temperature gradient is still very high on the solid electrolyte tube, which reduces the service life of the measuring probes equipped with these

  protection devices (Patent Applications in

  Federal Republic of Germany DE-OS 24 52 924; DE-AS 25

53,212).

  On another type of protection device, two perforated protection tubes were fixed around the solid electrolyte tube, these two tubes being arranged coaxially and at a distance from each other and their perforations being thus,

  from one tube to another (Patent Application in

  Federal Republic of Germany DE-OS 23 48 505).

  These protective devices have proved to be appropriate to a certain extent in

  as means of protection against the mechanical

  and against temperature and pressure shocks

  if we; however, from the point of view of the life of the measuring probe and its

  a catalyst because of the time gradients

  high temperatures between the most exposed

  exhaust emissions and that which is only

  properly exposed to these exhaust gases, and other

  especially because they can not prevent the inactivity

  catalytic inactivation by catalytic

  such as sulfur, phosphorus and in particular lead and lead compounds when

of the essence that contains it.

  Vehicles equipped with such measuring probes must therefore use unleaded gasoline, a restriction which limits their range of action being

  unleaded gasoline is not everywhere

ponible.

  The invention therefore aims at creating

  protection device for measuring probes.

  sure that protects them not only from mechanical actions and thermal shocks and pressure but

  also guaranteeing a satisfactory life expectancy

  of the measuring probe, especially when

  exhaust gases contain lead.

  Surprisingly, it was found that when a sintered tube was used as a protective device, the occurrence of an inactivation of the measuring probe by inhibition of the measurement was virtually ruled out for a long time. layer of cata-

  lyser with compounds containing sulfur, phosphorus

  phore or even lead (when a fuel containing

this metal is used).

  As materials in which can be

  The sintered tube is made of ceramic materials

  such as Sillimanite, Cordierite, Silika, corundum, Forsterite, but especially metals and alloys such as SICA-R (1.4404 or 316), inconel, incoloy, titanium, metal Monel, nickel. Highly alloyed metals such as inconel, incoloy, or nickel are preferably used because they are particularly resistant to temperature loads of 9000 and higher, as well as to vibrations.

  gases and high thermal and mechanical loads.

  The wall thickness of the tube

  sintered material should not be less than

  ceramics and at lmm for metals. When the thick

  wall thickness exceeds 20mm, there is no practical improvement in the protective effect; only increases the time taken by the exhaust gases to pass through the body of sintered material, which causes the increase of the response time of the probe. The wall thicknesses to be preferred are between

  2 and 6 mm, because they combine a good effect of pro-

  tection at a short response time.

  As regards the pore size of the sintered material tube, it is advantageous

  that it is between 20 and 200 p. When the fat

  pore size exceeds 800 u, the protective effect

  is too weak Below 5 p, the speed of the

  flow decreases sharply, which has the effect of increasing

  also strongly reduce the response time. Reduced pore size allows for reduced wall thickness, as the protective effect increases

  when the pore size decreases.

  A reduced wall thickness can

  partially compensate for a steady flow velocity

  pick. The preferred pore size is between

  40 and 80 y, because a particularly advantageous compromise

  is then made between the size of the tube, the

  separation, the creep resistance, the durability

  mechanical capacity and the flow time of gases through

to the sintered material.

  The internal faces of the pores of the body of sintered material can also be covered

  a catalyst material (for example by impregnating

  which accelerates the introduction of the gas balance. This catalyst can be constituted by a

  rare metal, for example by a platinum group metal.

  This has the advantage of obtaining in a simple manner and practically without additional expense (if the impregnation is ignored) a sufficiently long contact time to bring the components of the exhaust gases to a thermodynamic equilibrium, a precondition of obtaining, with such measuring probes, when \ = 1,000, a jump of potential having the desired slope when one passes from the reducing state to the state

oxidant and vice versa.

  The construction of such tubes in

  sintered material is generally known and can only be

  there is no hidden difficulty for the person skilled in the art who

  treprend. The connection of the body made of sintered material

  to the body of the measuring probe can be directly

  -6- by welding, soldering, threaded connection or gluing

  on the ceramic of the exhaust gas probe.

  The body of sintered material can also be removably mounted; it can thus possibly be exchanged as an inexpensive component before the protective effect ceases, which avoids having to replace the entire measuring probe, a component

of a certain price.

  In the figures, are represented

  two examples of execution. The figures

  trent successively: FIG. 1, in side view and in partial section, a measuring probe according to the invention, with protection device made of sintered material, FIG. 2, the end sector, on the exhaust pipe side, of a measuring probe according to the invention and equipped with a protection device made of sintered material, according to another embodiment, FIG. 3, the end sector, on the exhaust pipe side, of a measurement probe according to FIG. state of the art, equipped with a protective device.

  The electrochemical measuring probe

  shown in Figure 1 works according to the principle

  known pe of ion concentration solid electrolyte oxygen catena; it comprises a solid electrolyte tube 1 ion-conducting and closed on one side, stabilized cubic zirconia tube which, on its outer face, supports a catalyst layer 2

  platinum conductive electron and on its inner face

  an electron-conducting track 3 that penetrates

  down to the bottom zone of the solid electrolyte

  from and which is also platinum. The conductive track 3 is connected to a contact element, not shown, -7-

  in electrical connection with a plug 4. The elec-

  solid trolyte 1 is sealingly mounted in the

  longitudinal piercing 5 of a metal casing 6 for

  for the incorporation in an exhaust pipe, a male thread 7 and a hexagonal nut 8. At the end of the connection of the casing 6, is mounted a tube 9 provided with openings air inlet 10 allowing the ambient air to enter the empty space 11 of the

  electrolyte tube solidel.The end of the elec-

  solid trolyte located on the exhaust pipe side protrudes from the longitudinal piercing 5 of the box and is exposed to the exhaust gas located in

  this exhaust pipe. To protect the layer of

  Electron conductive catalyst 2 provided on the tube

  solid electrolyte 1 of an intensive denudation

  to avoid temperature and pressure shocks

  consecutive to the direct impact of the flue gas

  the protective device 12 in accordance with the

  The invention, made of a sintered material, has been fixed by welding to the box 6 around the portion of the solid electrolyte tube 1 protruding into the flow of

  exhaust gas. The tube of sintered material is dis-

  placed around the measuring probe and at a distance of between 0.01 and 20.0 mm. FIG. 2 shows another embodiment of a protection device according to the invention, which device is attached to the

  casing 6 via a thread 13.

  FIG. 3 shows a protection device corresponding to the state of the art and

  having a metal tube 14 having an opening

  15 for the entry of the exhaust gas.

  Thanks to the porous body of fried

  As a result, only a portion of the exhaust gas stream and not all of it is passed through the pores to the measuring probe; thus, a bypass effect is practically achieved. The speed and speed of this

  flow of exhaust gas reaching the measuring probe

  re can be adjusted simply by choosing the thickness

  partition and the size of the body's pores

  sintered material and adapt to the conditions

  Rees. The body made of sintered material makes it possible

  maintain a temperature balance of the probe.

  Thermal shock and pressure peaks do not reach

  the ceramic of the probe (solid electrolyte

  of). When the temperature of the gases is low, that is to say when an engine idles, the temperature of the measuring probe falls less quickly a probe equipped with the protective device according to

  to the invention therefore enters less rapidly into

  that a probe corresponding to the state of the art

  than. Because of the bypass effect of the porous material of sintered material, it reaches the measuring probe only a relatively small gas flow rate; as a result, the heating of the probe is also relatively simple, which is an advantage in starting at

  cold and, if necessary, idle. The body in

  sintered material opposing a damping effect to. temperature peaks and pressure peaks, the probe can be mounted closer to the motor, which reduces the response time. The slight delay with which the flow

  gas reaches the measuring probe, delay due to its

  wise through the porous body made of sintered material, can

  by this measure be easily compensated.

The effectiveness of the pro-

  tion according to the invention is shown by the example

ple who follows.

A measuring probe of trade

  stabilized zirconia, provided on both sides with

  -9- tacts of precious metal, was surrounded by a device

  in accordance with the invention (that of FIG.

  re 1). The protective device was made of SIKAR sintered material (material NO: 1.4404), had a wall thickness of 3.0 mm and a pore size of 80 percent.

  The measuring probe equipped with the dis-

  positive protection according to the invention was expo-

  45 mm to the exhaust gases of a spark ignition engine. This engine used 81 gas

  on time. Gasoline contained 0.15 g of lead per liter.

  During this period, there was virtually no noticeable increase in response times for the poor mixture-rich mixture or mixture-poor mixture voltage jump. A determined tension

  corresponding to the air-fuel ratio (Q

held steady.

The measuring probe kept its

  good sensitivity, which comes from the fact that

  necessary to produce a specific voltage

  (Ä% = 0.98) remained almost constant.

  All values are within the margins specified by the manufacturer for a new probe

  (without the protective device according to the invention

  tion). The results are recorded in the following table:

BOARD

  In accordance with the manufacturer's specified tolerance (Fig. 1) Test duration (h) 0 45h Response time at 350 C 200 240 400 for voltage jump (ms) Rich mixture at 550 C 20 lbs. Lean mixture (600400mV) (ms) Response time at 350 C 18 30 65 for voltage jump (ms) Lean mixture at 550 C 12 40 <40 rich mixture (400-600mV) at 500mV 1. 012 1.014 from 1.003 to 1.018 Temperature for s = 500mV 230 235 265 o! - O ru>% I t C

- -11-

  To allow a comparison, a probe of

  measurement without protective device in accordance with the

  has been exposed to the exhaust gas flow. After

  only three hours, the maximum voltage indicated ini-

  the measurement probe fell from 900 mV to about 400 mV, ie after three hours

  measurement without protective device was put out of

vice. -12-

Claims (9)

  1. Electrochemical measuring probe for determining the oxygen content of gases   exhaust systems, in particular from engines with   internal combustion, the part of which is exposed to   is surrounded by a protective device arranged around and at a distance from the measuring probe and having openings, characterized in that the protective device (12) consists of   a tube of porous sintered material. 2. Measuring probe according to the   1, characterized in that the material sintered (12) is metal. 3. Measuring probe according to the   2, characterized in that the tube   sintered material (12) is made of resistant nickel alloys at high temperatures. 4. Measuring probe according to one of the   claims 1 to 3, characterized in that the   tube of sintered material (12) is arranged around the measuring probe and at a distance of 0.01 to 20.0 mm of it. 5. Measuring probe according to one of the   claims 1 to 4, characterized in that the   tube walls of sintered material (12) made of metal have a   thickness between 1 and 20 mm. 6. Measuring probe according to one of the   claims 1 and 4, characterized in that the   sintered material (12) is ceramic. 7. Measuring probe according to the   6, characterized by the fact that the walls of the   tube made of sintered material (12) made of ceramic have a thick between 1.5 and 20 mm.   -13- 8. Measuring probe according to one of the   claims 1 to 7, characterized in that the   The pores of the tube of sintered material (12) have a size of 5 to 800 p. 9. Measuring probe according to one of the   claims 1 to 8, characterized in that   inner surfaces of the pores of the sintered material tube (12) are covered with a catalyst material   accelerating the equilibrium of the gases.