Electric heating device for an exhaust gas catalyst

Abstract

The invention provides an electric heating device (1) for an exhaust gas catalyst. The electric heating device comprises a sleeve (10) and a heated honeycomb structure (20) contained within the sleeve (10). The electric heating device (1) is adapted to be positioned in a section of an exhaust gas pipe upstream of a catalyst, occupying a cross-section of said section so that exhaust gases flowing in the pipe pass through the honeycomb matrix before reaching the catalyst. The electric heating device further comprises a heated honeycomb structure (20) having a spiral winding around an axis AA, and having a predetermined number of windings around said axis AA. Said heated honeycomb structure (20) is adapted to have internal inductance. Figure 2

Description

Title of the invention: Electric heating device for an exhaust gas catalyst. Technical field

[0001] The present application relates to an electric exhaust gas catalyst heating device, positioned upstream of the catalyst in an exhaust pipe, and adapted to heat the exhaust gases to bring them to an effective catalysis temperature. Previous technique

[0002] A three-way catalytic converter in a gasoline vehicle has an effective operating range for temperatures above 400°C, whereas a diesel vehicle emissions control system has an effective operating range from approximately 180°C. A diesel vehicle emissions control system typically includes an oxidation catalyst that treats hydrocarbons (HC) and carbon monoxide (CO), a selective reduction catalyst that treats nitrogen oxides (NOx), and a particulate filter.

[0003] When the engine is cold, the exhaust gas temperature is initially low, and it takes some time for it to rise to an effective operating temperature for the catalyst. This means that during the entire period when the exhaust gas temperature is too low, the gases are not properly filtered by the catalyst.

[0004] The same problem exists for diesel engines, which take longer to warm up than gasoline engines. Therefore, if the driver is traveling at low speeds with a lightly loaded vehicle, the exhaust gases may remain below the effective catalytic temperature for a potentially long period. This problem of exhaust gas temperatures below the effective temperature can also occur if, after driving on the highway, the vehicle returns to driving in urban areas with a light load.

[0005] Also for hybrid vehicles, the internal combustion engine cools down when the electric motor is in operation for a sufficient amount of time, and the same exhaust gas temperature problem arises when the internal combustion engine is restarted.

[0006] To solve this problem, it is known to position a heating device upstream of the catalyst. This heating device can take the form of a sleeve placed in an engine exhaust pipe, and containing a heated honeycomb matrix through which the gases pass to be heated before reaching the catalyst, thus improving the pollution control of the exhaust gases.

[0007] With reference to [Fig.1], the electric heating device 1 comprises a cylindrical sleeve 10 and a honeycomb structure 20 heated by the circulation of an electric current contained in the cylindrical sleeve 10.

[0008] The external diameter of the cylindrical sleeve 10 can correspond to the internal diameter of the exhaust pipe so that the electric heating device 1 can be positioned in a section of the exhaust gas pipe, occupying an entire cross-section of said section. Thus, the gases produced by the engine necessarily pass through the heated honeycomb structure 20 before reaching the catalyst.

[0009] Generally, the electric heating device 1 also includes a support device for the heating alveolar structure in the cylindrical sleeve 10, comprising for example a support structure 19 housed in the cylindrical 10, for example downstream of the heating alveolar structure 20, and retaining pads 24 holding the heating alveolar structure 20 against the support structure 19.

[0010] In prior art heating devices, the heating honeycomb structure 20 is obtained by winding, around an axis AA, which when the heating device is installed, is parallel to the direction of gas movement in the exhaust pipe (represented by arrow F on [Fig.1]), a heating honeycomb panel 21 on [Fig.1].

[0011] The heated honeycomb panel 21 comprises at least one metallic honeycomb matrix 23, which may be attached to a metallic support layer 22, or even positioned between two support layers 22. By honeycomb matrix 23, we understand a formation comprising a plurality of cells through which the exhaust gases can pass, the cells being delimited by metallic walls that heat up when an electric current is passed through them.

[0012] The heated honeycomb structure 20 also includes electrical connectors (not shown) for passing a current through the heated honeycomb structure 20 to heat it. The structure is arranged such that one end of the metal support wall is connected to a first electrical connector and a second end of the metal support wall is connected to a second electrical connector, so that the current flows through the entire metal support wall and the honeycomb matrix mounted on the wall.

[0013] The current flowing in the metallic support wall, and therefore in the heated honeycomb matrix 20 and also in the heated honeycomb panel 21, heats the exhaust gases by Joule heating. Activation of the heated honeycomb structure 20 is achieved, for example, by a simple signal control. active / not active or using a control signal of the type Pulse Width Modulation (PWM).

[0014] Since the heated alveolar structure 20 exhibits resistive load behavior, its activation results in a sharp increase in current within said heated alveolar structure 20, an increase that is as rapid as the increase in voltage across the terminals of the heated alveolar structure 20. This rapid current variation is generated by the very structure of the vehicle's electrical heating device 1, i.e., the battery, the battery connections to the vehicle components, and the connecting capacitors.

[0015] This very high current draw causes a very sudden and significant drop in the vehicle's battery voltage. Thus, in the case of a 48V battery in a hybrid vehicle, this current draw causes a significant drop in the vehicle's electrical system voltage, which can lead to failures of the vehicle's electronic components or premature aging of the components and coupling capacitors.

[0016] To solve this problem, it would therefore be necessary to time-shift the voltage surge from the current surge. Due to the winding of the prior art honeycomb structure 20 and the values ​​of the coupling capacitances, it would be necessary to use an external inductor with a very high value on the order of 1 x 10⁶ Henry. Such an external inductor would be very large, leading to integration and cost issues. Summary of the invention

[0017] The invention aims to remedy the disadvantages of the prior art described above.

[0018] In particular, an object of the invention is to propose a heating device which, thanks to an advantageous winding of the alveolar structure, makes it possible to dispense with the addition of an external inductance to compensate for the presence of an equivalent inductance of a control device of the heating device.

[0019] In this regard, the invention proposes an electric heating device for an exhaust gas catalyst, the electric heating device comprising a sleeve and a honeycomb structure heated by electric current circulation, contained within the sleeve, the electric heating device being adapted to be positioned in a section of an exhaust gas pipe upstream of a catalyst, fully occupying a cross-section of said section so that exhaust gases flowing in the pipe pass through the honeycomb matrix before reaching the catalyst, the electric heating device being characterized in that the heated alveolar structure has a spiral winding around an axis AA, comprises a determined number of windings around said axis AA and said heated alveolar structure is adapted to exhibit an internal inductance.

[0020] Thanks to the invention, it is now possible, without adding external inductance, to counterbalance the equivalent inductance of the control circuit in order to obtain a sufficient time lag between a control voltage and a control current when the heating device is activated.

[0021] For example, in one embodiment of the invention, the spiral winding around an axis AA of the heated alveolar structure has a first end and a second end, adapted to receive a control signal and allowing a reliable electrical connection between the heating device and the heated alveolar structure.

[0022] Advantageously, the invention proposes to control the value of the internal inductance of the heated alveolar structure that the number of windings around said axis AA is between 2 and 10 windings.

[0023] For example, the internal inductance of the heated alveolar structure has a value between 0.5.106 Henry and 1.106 Henry.

[0024] In order to optimize the efficiency of the heating device, the heating alveolar structure is composed of at least two materials having different resistivities.

[0025] For example, the catalytic element is disposed in the sleeve, downstream of the heated alveolar structure with respect to the direction of flow of the exhaust gases.

[0026] Alternatively, the catalytic element is of the oxidation catalyst type, LNT, or three-way.

[0027] In a second aspect of the invention, an exhaust gas catalysis assembly is proposed comprising at least one catalyst and an electric heating device in which the catalyst is chosen from the group consisting of: - a three-way type catalyst, - an oxidation catalyst, - an LNT type catalyst, - a selective reduction catalyst.

[0028] In a third aspect of the invention, a vehicle is also proposed, comprising a heat engine, an exhaust duct for exhaust gases produced by combustion in the heat engine, a catalyst disposed in the exhaust duct, and an electric heating device disposed in the duct exhaust, upstream of the catalyst relative to the direction of exhaust gas flow in the exhaust pipe. Brief description of the drawings

[0029] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analysis of the accompanying drawings, on which:

[0030] [Fig.l], already described, schematically represents a catalysis system according to the prior art.

[0031] [Fig.2] schematically represents a catalysis system according to one embodiment of the invention. Description of the implementation methods

[0032] With reference to [Fig. 2], we will now describe an electric heating device 1, forming part of a vehicle catalytic converter assembly comprising an internal combustion engine (not shown), the internal combustion engine being of the gasoline or diesel type. Preferably, the vehicle may also be a hybrid vehicle. The catalytic converter assembly includes a catalyst disposed in an exhaust pipe for gases generated by combustion in the engine, and adapted to filter the exhaust gases before their release into the atmosphere.

[0033] Depending on the type of engine, the catalyst may be a three-way catalyst (typically for gasoline engines), which reduces nitrogen oxides, oxidizes carbon monoxide, and oxidizes unburned hydrocarbons. It may also be a DOC (Digital Oxidation Catalyst) for CO and HC, or an LNT (Lean NOx Trap) catalyst, which is both an oxidation catalyst and a NOx storage and reduction catalyst, or a selective reduction catalyst, or an assembly comprising an oxidation catalyst followed by a selective reduction catalyst, etc.

[0034] The electric heating device 1 is located in the exhaust pipe, upstream of the catalytic converter, i.e., between the engine outlet and the catalytic converter inlet. The sleeve may also include connection lugs 31 adapted to receive a first electrical connector E1 and a second electrical connector E2 of the heating honeycomb structure 20 and hold them in a fixed position so that they can be connected to a generator via suitable connectors. The first electrical connector E1 and the second electrical connector E2 are not visible in the drawings but are known to those skilled in the art.

[0035] Advantageously, the heated honeycomb structure 20 is adapted to have a spiral winding around an axis AA. Here, a spiral winding is understood to be a winding that follows a curve starting at a central point. then moves further and further away, while at the same time it rotates around it along the cutting axis BB on the [Fig.2].

[0036] Thus, thanks to this particular winding, the heated alveolar structure 20 has a controlled inductance dependent on the number of windings, making it possible to obtain a desired and controlled time lag between a control current and a control voltage circulating in the heated alveolar structure 20 and the vehicle's electrical control circuit when a control signal is applied.

[0037] In a particular embodiment, it is made with between 2 and 10 turns of winding, preferably 4.

[0038] Thus, it is possible to obtain from the heated alveolar structure 20 an inductive behavior allowing to balance the equivalent inductance of the control circuit without adding an external inductance type electronic component and thus allowing an optimization of costs but also an improvement in the reliability of the electronic control device.

[0039] Advantageously, it is possible to integrate two heated honeycomb structures 20 one after the other in the exhaust pipe, upstream of the catalyst, that is to say between the engine outlet and the catalyst inlet. Advantageously, in one embodiment, the two heated honeycomb structures 20 are connected in series in order to double the value of the internal inductance obtained.

[0040] Thus, thanks to the invention, it is possible to obtain an internal inductance of the heated alveolar structure 20 of the same order as that of the vehicle's connector linking the battery to the electric heating device 1 allowing an optimization of the time lag between the current and the voltage in the heated alveolar structure 20 during an activation of said electric heating device 1.

Claims

Demands

1. Electric heating device (1) for an exhaust gas catalyst, the electric heating device comprising a sleeve (10) and a heated honeycomb structure (20) by electric current circulation contained in the sleeve (10), the electric heating device (1) being adapted to be positioned in a section of an exhaust gas pipe upstream of a catalyst, fully occupying a cross-section of said section such that exhaust gases flowing in the pipe pass through the honeycomb matrix before reaching the catalyst, the electric heating device being characterized in that the heated honeycomb structure (20) has a spiral winding around an axis AA, has a determined number of windings around said axis AA and said heated honeycomb structure (20) is adapted to have an internal inductance,and in that the heated alveolar structure (20) is composed of at least two materials having different electrical resistivities.

2. Electric heating device (1) of exhaust gas catalyst according to claim 1, characterized in that the spiral winding around an axis AA of the heating honeycomb structure (20) has a first end and a second end, adapted to receive a control signal.

3. Electric heating device (1) for exhaust gas catalyst according to claim 1 or claim 2, characterized in that the number of windings around said axis AA is between 2 and 10 windings.

4. Electric heating device (1) of exhaust gas catalyst according to any one of claims 1 to 3, characterized in that the internal inductance of the heating honeycomb structure (20) has a value between 0.5.106 Henry and 1.106 Henry.

5. Heating device according to any one of the preceding claims, further comprising a catalytic element disposed in the sleeve, downstream of the heating alveolar structure (20) with respect to the direction of exhaust gas flow.

6. Heating device according to the preceding claim, wherein the catalytic element (19) is of the oxidation catalyst type, LNT, or three-way.

7. Exhaust gas catalysis assembly comprising at least one catalyst and an electric heating device (1) according to any one of the preceding claims, wherein the catalyst is selected from the group consisting of: - a three-way type catalyst, - an oxidation catalyst, - an LNT type catalyst, - a selective reduction catalyst.

8. Vehicle, comprising a heat engine, an exhaust duct for exhaust gases produced by combustion in the heat engine, a catalyst disposed in the exhaust duct, and an electric heating device (1) according to any one of claims 1 to 6 disposed in the exhaust duct, upstream of the catalyst with respect to the direction of flow of the exhaust gases in the exhaust duct.