JP3017545B2 - Heating apparatus and heating control method for automotive catalytic converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating device and a heating control method for a catalytic converter for an automobile, in which a metal carrier of the catalytic converter is energized and heated.

[0002]

2. Description of the Related Art Catalytic converters are widely used for purifying exhaust gas from automobiles and the like. Catalytic converters for automobiles, purifies CO in the exhaust gas, the HC and NO _x oxidation or reduction to. Pt, Rh, Pd or the like is used as a catalyst. Recently, metal carriers have been employed in catalytic converters. The metal carrier is obtained by supporting a catalyst on a honeycomb made of a metal foil such as a stainless steel foil. The catalyst does not function unless it is at a certain temperature or higher, for example, at 350 ° C. or higher. On the other hand, as environmental pollution on a global scale becomes more serious, exhaust gas regulations for automobiles are becoming more stringent. For this reason, the emission of unpurified gas from the start of the engine until the catalyst functions (for example, for 0.5 to 1 minute) is also a problem. Therefore,
A method has been proposed in which the metal carrier is directly energized to heat the catalyst until the temperature reaches a temperature at which the catalyst functions. For example, in an energized heat-generating catalytic converter disclosed in Japanese Utility Model Application Laid-Open No. 63-67609, an energizable metal monolith catalyst in which alumina is coated on a metal carrier close to the upstream side of a ceramic main monolith catalyst is provided. ing.
One electrode for energization is provided on the central axis of the metal monolith catalyst, and the outer cylinder of the metal monolith catalyst is used as the other electrode.

[0003]

When the metal carrier is directly energized, the metal carrier can be efficiently heated by Joule heat. Normally, 1
A 2 V battery is used. In addition, 3
In order to heat the metal carrier to 50 ° C. or more, it is necessary to control the heating current in a wide range from 0 to several hundreds A. When an electromagnetic switch is used to control the heating current, a large-scale device is required for arc extinction and the like. Further, a method of inserting an SCR or other semiconductor element into the heating circuit and changing its resistance value is conceivable. However, in this method, the resistance heating of the element is large, and it is necessary to consider the cooling of the element. In addition, the catalytic converter may not function properly while driving a vehicle. For example, when a low-speed rotation is performed due to a signal or the like, or when an engine brake is applied on a downhill, the exhaust gas temperature decreases. As a result, the metal carrier is cooled by the exhaust gas passing through the inside of the catalytic converter, and the catalyst does not function. Also in such a case, unpurified exhaust gas is released to the atmosphere as in the case of starting the engine.

Accordingly, the present invention provides a heating device for a catalytic converter for automobiles which can heat a metal carrier in a short time with high energy efficiency and which does not give audible frequency noise to audio equipment and has excellent durability. An object of the present invention is to provide a method for heating a catalytic converter for an automobile, which can maintain the catalytic converter at a required temperature even when the engine speed decreases during operation.

[0005]

A heating device for an automotive catalytic converter according to the present invention is a device for directly energizing and heating a metal carrier of a catalytic converter by supplying power from a battery, wherein a parallel connection is provided between the battery and the catalytic converter. And a current-controlled oscillation circuit for turning on and off the power MOSFET at a preset time ratio and at a frequency of 15 kHz or more. The number of power MOSFETs is determined by the rated current, the heating current supplied to the metal carrier, the heating time, and the like. For example, there are 5 to 30 pieces. The reference frequency of the current control oscillation circuit needs to be 15 kHz or more.
If the frequency is less than 15 kHz, audible frequency noise is given to audio equipment mounted on the car.

In a method for controlling heating of a catalytic converter for an automobile according to the present invention, in the method for electrically heating a metal carrier, a temperature of the metal carrier is detected, and the time ratio is set based on the detected temperature. Control the current. To detect the temperature of the metal carrier, a general temperature detector such as a thermocouple or a thermistor is used. The detected temperature is fed back to the current control oscillation circuit, the time ratio is set so that the metal carrier has a required temperature, and the average heating current is adjusted.

[0007]

The power MOSFET is turned on and off in response to a gate signal from the current control oscillation circuit, and outputs a pulsed heating current to the metal carrier. The magnitude of the heating power is adjusted by changing the pulse width of the heating current, that is, the time ratio. Therefore, heat generation in the power MOSFET is limited to a very short time at the time of on / off switching and is extremely small. The reason why the power MOSFET is used in the heating device of the present invention is that the time required for on / off switching is shorter than that of the SCR, and the heat generation is small. Further, since the detected temperature of the metal carrier is fed back to the current control oscillation circuit to control the heating current so as to reach the target temperature, the metal carrier is always kept at the catalyst functional temperature.

[0008]

FIG. 1 shows an example of a heating apparatus according to the present invention. The metal carrier of the catalytic converter 1 includes a honeycomb and an outer cylinder (both are not shown). In the honeycomb, a flat foil and a corrugated foil are overlapped to form a spiral. The flat foil and corrugated foil are made of 20Cr-5A with a thickness of 50 μm.
1. Made of stainless steel foil. The flat foil and the corrugated foil are brazed. The honeycomb was inserted and brazed into an outer cylinder made of 19Cr stainless steel. A battery (terminal voltage 12 V) 2 is connected to the catalytic converter 1 configured as described above. A heating current control circuit 3 is inserted between the catalytic converter 1 and the battery 2. The heating current control circuit 3 includes 20 power MOSFETs 4 connected in parallel and all power MOSFETs.
And a current control oscillation circuit 6 for simultaneously turning on and off T4. Since the rated current of the power MOSFET 4 is 50 A, a heating current of up to 1000 A can be supplied to the catalytic converter 1. In the current control oscillation circuit 6,
The control device 7 is connected. The control device 7 outputs a pulse width control signal to the current control oscillation circuit 6 to control the heating current. In the control device 7, a heating current pattern at the time of starting the engine, a target temperature of the metal carrier, and the like are set. A thermocouple 9 for detecting the temperature of the metal carrier is attached to the catalytic converter 1. The temperature signal detected by the thermocouple 9 is input to the control device 7.

Here, the operation of the heating device configured as described above will be described. FIG. 2 shows an example of a heating current pattern at the time of starting the engine. As shown in the diagram of FIG. 2, before starting the engine, the metal carrier is energized to preheat the metal carrier. The preheating current is 50 to 600 A, and the preheating time is about 5 to 30 seconds. When the engine is started after the preheating time has elapsed, the heating current is reduced by 20 to 40%.
About high. Immediately after the start of the engine, the exhaust gas is cooled by an exhaust manifold or the like, so that the temperature of the exhaust gas is low. As a result, unpurified exhaust gas is released into the atmosphere. Therefore, as described above, the heating current is increased to prevent the catalytic function from lowering. When the temperature of the metal carrier becomes 500 ° C. or higher, the power MOSFET 4 is automatically turned off by the temperature signal from the thermocouple 9, and the supply of the heating current to the metal carrier is stopped. Thereafter, the metal carrier is maintained at the catalyst functional temperature by the sensible heat of the exhaust gas and the reaction heat of the catalyst. Further, when the temperature of the metal carrier is lowered, for example, when the rotation speed becomes low due to a signal waiting, or when the engine brake is applied on a downhill, the thermocouple 9 detects this and outputs a temperature signal to the control device 7. I do. The control device 7 outputs a pulse width modulation signal to the current control oscillation circuit 6 and supplies a heating current from the battery 2 to the metal carrier.

Next, the operation results of the actual apparatus will be described. In the heating device described in the above embodiment, the power M
The time required to turn on and off the OSFET is extremely short, several hundred ns, and the heat generation in the transient state is slight.
There was no need to specifically cool the ET. Power MO
Since the SFET has no contact, it has sufficient durability.
It worked stably. By the way, when the heating current was controlled on and off by using an electromagnetic switch, the contact was melted and damaged by several tens of times of on and off, so that it could not be used. When a power transistor is used, a water-cooled copper plate is required for cooling the element.

[0011]

According to the heating device of the present invention, a plurality of power MOSFETs are connected in parallel, and the heating power is controlled by the ON / OFF time ratio. Power MOS
Since the time required to switch on and off the FET is extremely short, the temperature rise of the power MOSFET can be suppressed. As a result, the metal carrier can be heated in a short time with high energy efficiency. Further, according to the heating control method of the present invention, the detected metal carrier temperature is fed back to the current control oscillation circuit to control the heating current, so that the metal carrier is always kept at the catalyst functional temperature. Therefore,
The catalytic converter can be maintained at a required temperature even when the engine speed decreases during driving of the vehicle.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a heating device showing an example of the present invention.

FIG. 2 is a diagram showing an example of a heating current pattern at the time of starting an engine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Catalytic converter 2 Battery 3 Heating current control circuit 4 Power MOSFET 6 Current control oscillation circuit 7 Controller 9 Thermocouple

Continued on the front page (72) Inventor Shigeo Kawahara 1 Kimitsu, Kimitsu City, Chiba Pref. Nippon Steel Corporation Kimitsu Works (56) References JP-A-4-219413 (JP, A) William A. Whitten Berger et al. , "Recent Developments in Electrically Heated Metal Monoliths", SEA Technical Paper Series, U.S.A. SA , March 1990, 900503, p. 61-70 (58) Field surveyed (Int.Cl. ⁷ , DB name) F01N 3/20 F01N 3/24 F01N 9/00

Claims (2)

(57) [Claims] An apparatus for directly energizing and heating a metal carrier of a catalytic converter by supplying power from a battery,
A plurality of power MOSFETs connected in parallel between the battery and the catalytic converter; and a power MOSFET having a preset time ratio and a frequency of 15 kHz or more.
A heating device for an automotive catalytic converter, comprising: a current control oscillation circuit for turning on and off T. 2. A method for electrically heating a metal carrier by the apparatus according to claim 1, wherein a temperature of the metal carrier is detected, the time ratio is set based on the detected temperature, and an average heating current is controlled. A heating control method for an automotive catalytic converter.