JPH0633746A - Electric heating catalytic device - Google Patents

Abstract

PURPOSE:To favorably purify a harmful substance in exhaust gas to be changed to a harmless substance by efficiently activating an electric heating catalyst. CONSTITUTION:An electric heating catalytic device 20 has spiral foil 24 provided in an exhaust passage of an engine to generate heat by a supplied current and a catalyst 25 mounted on the foil 24 to be activated. Here by forming a plate thickness of the foil 24 in the central part thinner than in the external side part and by increasing a resistance value per unit length of the supplied current in the foil 24 larger as it advances to a central part of the catalyst 25, so as to increase a heating value supplied to the catalyst 25, exhaust gas from the exhaust passage is purified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrically heated catalyst device provided in an exhaust passage of an engine to activate an electrically heated catalyst.

[0002]

2. Description of the Related Art Conventionally, an electrically heated catalyst device has been studied which rapidly heats a catalyst immediately after the engine is started in order to reduce harmful substances emitted immediately after the engine is started. Such an electrically heated catalyst device 10 is, for example, as shown in FIG.
It is provided in the middle of the exhaust passage 13 interposed between the combustion chamber 12 of the engine 11 and the muffler 14, and a voltage is applied from a battery power source 17 to a carrier 15 which is a heating element via a switch 16 in an ON state. The carrier 15 is rapidly heated to activate the electrically heated catalyst mounted on the carrier 15 to remove CO (carbon monoxide), HC (hydrocarbons), etc. in the exhaust gas discharged from the combustion chamber 11. Had removed harmful substances.

[0003]

However, the above-mentioned electrically heated catalyst device is basically a uniform resistor and is uniformly heated by an electric current, but the heat generated in the outer peripheral portion is taken to the atmosphere. As a result, the amount of heat supplied to the catalyst is not effectively used. The present invention has been made in view of the above problems, and an object of the present invention is to provide an electrically heated catalyst device that can efficiently activate an electrically heated catalyst.

[0004]

In order to achieve the above object, according to the present invention, there is provided a heating element which is provided in an exhaust passage of an engine and which generates heat by a supplied current, and a heating element which is mounted on the heating element and which is heated. An electrically heated catalyst that is activated by, and an electrically heated catalyst device that purifies exhaust gas from the exhaust passage by the electrically heated catalyst,
There is provided an electrically heated catalyst device in which the resistance value of the supply current in the heating element per unit length is increased toward the central portion of the electrically heated catalyst to increase the amount of heat supplied to the electrically heated catalyst.

[0005]

For example, in a honeycomb type electric heating catalyst device using a spiral foil as a heating element, the thickness of the foil is made thinner in the central portion than in the outer portion, and the resistance value of the central portion of the electric heating catalyst in the heating element is reduced. By increasing
The heat generated by the heating element is increased at the central portion, and the amount of heat is supplied to the electrically heated catalyst.

Therefore, heat loss to the outer circumference can be prevented, and the electrically heated catalyst can be favorably heated, and the exhaust gas can be favorably purified.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings of FIGS. In the following examples, a honeycomb type electrically heated catalyst device using a spiral foil as a heating element will be described. FIG. 1 is a top view showing an embodiment of the electrically heated catalyst device according to the present invention. In the figure, an electrically heated catalyst device 20 includes a substrate 21 made of cordierite or a heat-resistant alloy, a central electrode 22 provided in the central portion of the device and an outer electrode 23 provided outside, connected to a battery power source (not shown). , The electrodes 22 and 23 are attached to the center electrode 22 at predetermined intervals and disposed in the base 21.
Spiral foil 2 which is heated by the electric current supplied from the
4 and a catalyst 25 mounted on the spiral foil 24
And a heat insulating material 26 provided inside the base 21.

FIG. 2 is a perspective view showing an embodiment of the spiral foil shown in FIG. In the figure, the spiral foil 24 has a plate thickness t that is thinner in the central portion on the side of the center electrode 22 than in the outer portion. The foil 24 is a kind of resistor, and the resistance value per unit length of the current path in the foil 24 becomes larger toward the central portion as the plate thickness becomes thinner toward the central portion. Along with this, the foil 24 generates heat with respect to the current supplied from the battery power source, and the heat generation increases as the vortex approaches the central portion. That is, the electrically heated catalyst device 20 is shown in FIG.
3 shows an equivalent circuit when connected to the battery power source 17 shown in FIG. 3, the electric heating catalyst device 20 becomes equivalent to the series-connected resistors R _{1 to} R _n, and the resistors R _{1 to} R _n are connected to the switch 16. Connected to the battery power source 17 of voltage E via Note that n is an arbitrary integer.

Here, when the electric current I supplied to the electrically heated catalyst device 20 is obtained,

[0010]

[Equation 1]

Here, R _{i is the} local resistance, and when the above equation (1) is substituted to obtain the total power generation amount W,

[0012]

[Equation 2]

Therefore, the local heat generation amount W _i is

[0014]

[Equation 3]

[0015] Therefore, it can be seen from the above equation that the local heat generation amount is proportional to the local resistance. As can be seen from this, the smaller the plate thickness of the foil 24 shown in this embodiment, the larger the local resistance value, and the higher the amount of heat generation during current supply. The catalyst 25 is formed by providing a thin layer called a washcoat made of transition alumina, a promoter and a stabilizer on a platinum group metal, for example.

Therefore, in this embodiment, since the thickness of the foil 24 is made thinner toward the central portion, the resistance value of the foil 24 near the central portion of the apparatus is increased and the heat quantity at the time of current supply is increased. It is possible to prevent heat loss to the outer periphery, which allows the electrically heated catalyst 25 to be efficiently heated and activated, and is discharged from the combustion chamber of the engine (not shown) to the exhaust passage. It becomes possible to satisfactorily purify harmful substances in the exhaust gas flowing in the direction into harmless substances.

FIG. 4 is a perspective view showing another embodiment of the spiral foil shown in FIG. In the figure, foil 2
In No. 4, the plate width L is smaller in the central portion on the side of the central electrode 22 than in the outer portion. This allows the foil 24
As in the case of FIG. 2, the resistance value per unit length of the current path in the foil 24 increases as it approaches the central portion, so that heat generation increases.

Therefore, in this embodiment, since the plate width of the foil 24 is made smaller toward the central portion, the amount of heat in the vicinity of the central portion of the device at the time of current supply is increased, as in the above embodiment.
It is possible to prevent heat loss to the outer circumference, which enables efficient heating and activation of the electrically heated catalyst,
It is possible to satisfactorily purify harmful substances in the exhaust gas discharged from the combustion chamber of the engine (not shown) into the exhaust passage into harmless substances.

[0019]

As described above, according to the present invention, a heating element which is provided in the exhaust passage of the engine and which generates heat by the supplied electric current, and which is attached to the heating element and is activated by heating. In an electric heating catalyst device having an electric heating catalyst for purifying exhaust gas from the exhaust passage by the electric heating catalyst, a resistance value per unit length of a supply current in the heating element is set to a central portion of the electric heating catalyst. Since the amount of heat supplied to the electrically heated catalyst is increased by increasing the amount, the electrically heated catalyst can be efficiently activated.

[Brief description of drawings]

FIG. 1 is a top view showing an embodiment of an electrically heated catalyst device according to the present invention.

FIG. 2 is a perspective view showing an embodiment of the spiral foil shown in FIG.

3 is a diagram showing an equivalent circuit of the electrically heated catalyst device shown in FIG.

FIG. 4 is a perspective view showing another embodiment of the spiral foil shown in FIG.

FIG. 5 is a diagram for explaining a mounting state of the electrically heated catalyst device.

[Explanation of symbols]

 10, 20 Electric heating catalyst device 11 Engine 12 Combustion chamber 13 Exhaust passage 15 Carrier 17 Battery power source 21 Base 22,23 Electrode 24 Foil 25 Catalyst 26 Insulation material

Claims (1)

[Claims] 1. An electric heating apparatus, comprising: a heating element which is provided in an exhaust passage of an engine and which generates heat by an electric current supplied; and an electric heating catalyst which is mounted on the heating element and activated by heating. In an electric heating catalyst device for purifying exhaust gas from the exhaust passage by a catalyst, a resistance value per unit length of a supply current in the heating element is increased toward a central portion of the electric heating catalyst and is supplied to the electric heating catalyst. An electrically heated catalyst device characterized by increasing the amount of heat generated.