A DEVICE FOR CONTROLLING THE TEMPERATURE OF EXHAUST GASES IN MOTOR VEHICLES

Abstract: A device for controlling the exhaust gas temperature of motor vehicles at the catalyst location, in order to prevent overheating thereof, comprising a thermocouple (1), a control station (13) and a cable (3) terminated on a connector, for connection to the vehicle electrical system. The control station (13) is housed within a fluid-tight, cylinder-shaped, metal container (2) provided with two opposed axial passages (5, 6), while thermocouple (1) is directly connected to the input of the control station (13) through one (5) of said passages, and the cable (3) is directly connected to the control station (13) through the other (6) of the passages of the sealed container (2). The direct connection between the thermocouple (1) and the control station (13) may be performed through a thermocouple connection cable (15) provided with mineral insulation (20), or by means of a length of shielded cable (7) inserted between the minerally insulated thermocouple connection cable (15) and the control station (13).

Description: " A DEVICE FOR CONTROLLING THE TEMPERATURE OF EXHAUST GASES IN MOTOR VEHICLES " This invention relates to a device for controlling the temperature of the exha s gases of motor vehicles, in particular at the catalyst or catalytic muffler used for reducing the air pcllu-ing emissions. As it is known, catalytic mufflers are devices to be inserted in the vehicle exhaust pipe and include a porous separation wall provided with very small passages having a very large total surface area, and along which reactions of gas combustion completion take place, before the gases are exhausted to the environment. Said reactions tend to further increase the muffler temperat¬ ure, and there is a chance that the muffler gets damaged to an irreparable extent. Therefore, it is necessary to monitor the temperature continuously, at the muffler, and this is presently per¬ formed by means of a thermocouple inserted in heat ex¬ change relationship with the muffler, and connected, by means of a shielded lead wire, to a control station located in a reduced temperature area, to said control station there being terminated two or more electrical leads which, at the opposite end, are terminated onto a connector. When one or more predetermined temperature thresholds are exceeded, said control station (which has been calibr¬ ated depending upon the type of vehicle) provides a switching between the leads, or it generates an alarm signal for the driver, warning about a situation which may lead to muffler damage. For instance, the connector may be connected to the battery and to a warning lamp on the dashboard, which gets lit intermittently starting when a first temperat- ure threshold is reached, and with a continuously in¬ creasing intermittent frequency. Suitable signals for providing these functions are obtained in a known manner , based upon the voltage generated by the thermo¬ couple. Possibly, if a maximum threshold is exceeded, corresponding to a chance that the vehicle catches fire, the operation of the engine is inhibited. Known devices of this kind, although they are simple in construction and generally reliable, are nevertheless affected by some drawbacks and limitations. In fact, from a construction standpoint, it is necessary to provide openings in the vehicle body for mounting the control station, and to connect the thermocouple, by means of electrical leads and connectors, to the control station, and the latter to the power supply and to the user. This implies manufacturing and assembly costs which cannot be disregarded, and an unsatisfactory reliability, due to the presence of connections which can deteriorate. In addition, from an operation standpoint, problems may arise due to disturbances picked-up by the low power signal, and to compensation errors of the probe cold joint. It is an object of this invention to overcome the limit- ations and the drawbacks of the state of the art, as mentioned above, and in particular to provide a reduced cost and improved reliability device. This invention attains these objects through a device for controlling the temperature of the exhaust gases from motor vehicles at the catalyst location, comprising a thermocouple, a control station electrically connected to said thermocouple, and at least two mutually electrical¬ ly insulated, and externally shielded lead wires, which are connected to the control station at one end thereof, while at the other end they are terminated to a connect¬ or, characterized in that the control station is housed in an elongated fluid- tight metal container provided with two opposed axial passages, and in that said thermocouple is directly connected to the input of the control station through one of said passages. while said lead wires are directly connected to the control s.tation and come out from the second passage of said sealed container. According to a preferred embodiment, the direct connect¬ ion of the thermocouple to the control station is provid¬ ed through . minerally insulated thermocouple connect¬ ion cable. The above features and further ones will become appar- ent, together with the related advantages, from the following description of some preferred but non limiting embodiments of the control device of this invention, referring to the following drawing, wherein: Figure 1 is a schematic view showing the construction of the device according to the invention; Figure 1A is a cross-section taken along line A-A of Figure 1; Figure 2 shows an -alternative embodiment of the device; and Figure 3 is an electric circuit diagram of the connect¬ ions to the device of this invention. Referring now to Figure 1 , the device of this invention includes a temperature probe 1, in particular an insul¬ ated hot joint type "K" CHROMEL-ALUMEL thermocouple, to be inserted in the vehicle exhaust pipe. Said thermo- couple has an elongated construction, is provided with a nose-shaped seal fitting 12 and a fastening cap 11 in the lower portion thereof, and at the top thereof it includes a portion 15 comprising a minerally insulated cable which houses the pair of thermocouple leads, provided for the electrical connection to the. control station to be described below. According to this invention, control station 13 which controls the device operation and is shown schematically in broken lines, is housed within a sub¬ stantially cylindrical metal container 2, made for instance of galvanized steel, and provided with a pair of opposed axial passages 5, 6. The container is sub- stantially fluid-tight, in particular liquid-tight, and thermocouple 1 is directly connected to the control station entrance through passage 5. The expression "directly connected" as used herein and in the following should be understood as a synonym of a permanent connect- ion, free of intermediate connecting members. Figure 1A shows the structure of cable 15 comprising a pair of leads 16 and 17 provided with sheaths 18 and 19, surrounded by a mineral insulation 20 filling up cylindrical body 15. At the opposite end of lead 2, through axial passage 6, there comes out an extension cable 3 comprising two or more leads terminated on a connector 4 for connection to the alarm circuit and to the on-board electrical system which supplies power to the probe circuitry. Said circuitry which is preferably comprised of SMD integrated devices, is able to start switching operat- . ions or signals on the leads of cable 3 according to the temperature level indicated by the thermocouple which provides voltages in the range of some tens of mV. A relevant example will be described in the following, referring to Figure 3. A coil spring 10 is provided in coaxial position around cable 3, at the control station output, in order to prevent extension cable 3 from being kinked close to container 2. According to the alternative embodiment shown in Figure 2, wherein the same reference numbers have been used to indicate parts being identicalor corresponding to those shown in Figure 1, the direct connection between thermocouple 1 and control station 13 is provided through a further length of compensated extension cable 7, inserted between the minerally insulated thermocouple connection cable 15 and control station 13. Said externally shielded cable is a polymer insulated conventional type cable. The wires thereof are soldered and the joint is housed within a resin sealed socket or metal transition piece 8 which provides rigidity and protection. Extension cable 3 is comprised of four leads and is terminated to a connector 9 provid¬ ed with as many terminals. The above described construction provides a higher flexibility in locating the control station , which may be housed in a position further away from high temperature areas. However, in general, the length of shielded cable 7 ranges from 20 cm to 2 meters, with a thermocouple length in the range of 10 cm to 1 meter. Figure 3 shows an electrical circuit diagram of a device according to this invention, wherein the same reference numbers of the previous Figures have been used to show identical or equivalent parts. As it may be seen in the diagram, the control station 13 is connected to thermocouple 1 on one side, and on the other side, by means of four insulated leads A, B, C and D, protected by a shield 14, it is connected a four-way connector 9. As it is shown in the diagram, lead A is grounded at 21 on the vehicle, while lead C is connected to the battery positive terminal +V (in the case of negative grounding connection) through antitheft switch 22. Furthermore, the battery positive terminal is connected to an optical warning device 23, for instance an electric bulb. The opposite end of the optical warning device is connected to lead B. When the probe temperature is lower than a first threshold, lead B is insulated from the ground, and lamp 23 is off. When the first temperature threshold is ex¬ ceeded, lead B gets intermittently grounded, with a frequency which is proportional to the temperature measured by the probe, whereby it causes the lamp to light up intermittently, with a frequency increasing according to the temperature. As it is shown in Figure 3, a fourth lead D may also be provided, to be actuated when an auxiliary threshold is reached, for instance at a temperature exceeding 1000° C. As it should be apparent to those skilled in the art, other constructions, arrangements and operation modes are of course possible. The advantages provided by the control device of this invention should be apparent from the above description. In fact, the device does no longer require the control station to be fastened to the vehicle body and does away with one component (the thermocouple-control station connector) and, in one embodiment it does away with the extension cable as well, whereby manufacturing and assembly costs are reduced. Furthermore, the device has a higher disturbance reject¬ ion capacity in that the shielding becomes integral between the thermocouple and control station, i.e. in the area where the signal level is weak. In addition, the compensating errors at the cold joint, which are liable to occur in the known devices, which are not easily predictable and which sometimes cause errors higher than the tolerance allowances, are completely eliminated. While this invention has been described referring to particular and preferred embodiments, it should be understood that it is in no way limited to what has been described herein, but it includes further variations and modifications which may be apparent to those skilled in the art.

Claims: CLAIMS 1. A device for controlling the temperature of motor vehicle exhaust gases at a catalyst location, comprising a thermocouple (1) , a control station (13) electrically connected to said thermocouple, and at least two mutual¬ ly insulated and externally shielded electrical leads, . which are connected to said control station (13) at one end thereof, while at the other end they are terminated on a connector (4, 9) , characterized in that the control station (13) is housed within an elongated fluid- tight metal container (2) provided with two opposed axial passages (5, 6) , and in that said thermocouple (1) is directly connected to the input of the control station (13) through one (5) of said passages, while said lead wires are directly connected to the control station(13) and come out from a second,passage(6) of said sealed contain¬ er (2) . 2. The device of claim 1, characterized in that said direct connection of said thermocouple to the control station (13) is performed through the thermocouple connection cable (15) provided with mineral insulation (20). 3. The device of claim 1, characterized in that said direct connection between the thermocouple (1) and the control - 1 1 - station (13) is provided through a length of a shielded cable (7) inserted between the minerally insulated thermo¬ couple connection cable (15) and the control station. 4. The device of claim 3, characterized in that the junction between said length ' of shielded cable (7) and the thermocouple insulated cable (15) is protected by a resin-sealed metal transition piece (8) . 5. The device of any claim 1 to 4, characterized in that it is provided with at least three lead wires ( A,3,C ) for connection to the vehicle ground (21), to the terminal (+V) of the vehicle battery which is not grounded, and to a warning lamp (23) . 6. The device of claim 5, characterized in that it is provided'with a fourth lead wire (D) to be connected to the vehicle start-up system. 7. The device of claim 5 or 6, characterized in that said container (2) is made of galvanized steel and has a substantially cymindrical shape. 8. A device according to any one of the preceding claims, characterized in that it includes a coil spring (10) mounted coaxially around said leads, at the control station outout.

Inventors: NOLI CANZIO, NOLI, CANZIO
Applicants: TESTEL SPA, TESTEL S.P.A.
Application year: 1992
Main classification: G05D23
IPC codes: F01N3, G01K7, G05D23