DE19933654A1 - Arrangement for electrical heating of catalyzer has condenser circuit designed so that in open state of switching device, condenser circuit is charged up at 15-50 volts - Google Patents

Abstract

An arrangement for the electrical heating of a catalyzer has an energy supply unit (3,4), a condenser circuit (5) which is connected with the output of the energy supply unit and a switching device (6) which is connected between the condenser circuit and a heating device (8) of the catalyzer so that the condenser circuit is selectively connected with the heating device for the heating-up or separated from it for the charging up of the condenser circuit by the energy supply unit. The condenser circuit and the energy supply unit are designed so that in the open state of the switching device, the condenser circuit is charged up at a rated voltage of 15-50 volts and in the closed state of the switching device, outputs inside the first three seconds at least 75% of the stored energy to the heating device.

Description

The present invention relates to an arrangement for electrically heating a Catalyst according to the preamble of claim 1.

Catalysts are used in the exhaust pipe of motor vehicles for exhaust gas purification used. For this, three-way reduction and oxidation catalysts are known. The pollutants contained in the exhaust gas can only then from the catalyst be converted when the temperature of the catalyst reaches a certain minimum temperature of around 250 ° C. Is the temperature of the catalyst below this activation temperature, the catalyst is working Not.

After starting, the catalytic converter gradually heats up due to the exhaust gas from the Motors and reaches the required activation after a certain time temperature. However, if the engine temperature, such as. B. cold start is low, can take a relatively long time to reach the activation temperature pass away. In addition, a certain part of the exhaust gas temperature is caused by the Wall of the exhaust pipe absorbed.

For this reason, it has been proposed to use a sub in motor vehicles floor catalytic converter, which is usually in the vehicle area below the parking brake is arranged between the driver and the front passenger seat, a close-coupled kata Provide analyzer, which can thus be supplied with hotter exhaust gas, the faster heating and consequently a faster conversion effect leads.

However, increasingly stringent emissions regulations require even faster ones Conversion and thus an even faster heating of the catalyst to a to ensure reliable cleaning of the exhaust air.  

For this reason, the use of electrically heated Catalysts known. The following for the sake of simplicity as an e-catalyst designated electrically heated catalyst is usually disc-shaped a thickness of 10-15 mm and in front of the catalytic converter near the engine arranged. Inside is the e-catalyst, such as in the DE 196 40 577 A1 is described by a spiral wound flat Formed sheet metal, a corrugated sheet metal arranged in the space between is. At the ends of the flat metal sheet, a supply voltage of for example 12 V, which causes the heating effect. The Internal resistance of the e-catalyst is z. B. in the order of 0.1 Ω.

As is known, the energy supply of the e-catalyst takes place via a Battery which is applied to the heating device of the e-catalytic converter for heating becomes. By using such an e-catalyst, a faster Heating and thus a significantly improved conversion behavior achieved become.

When developing newer catalysts, they have to be designed in this way be that they meet the currently required limit values for the pollutant content of the catalyzed exhaust air significantly below, so that the catalytic converter Limit values even after aging caused by the operating time can adhere to. Currently, the development of electrical in particular heated catalysts worked, which after about 45 the activation temperature of approx. 250 ° C. This value is only very powerful To reach batteries. Another improvement in response time is below The use of batteries is not possible with reasonable effort.

In the publications DE-C2-44 21 066, JP-A-0 42 76111 and EP-A-0 533 037 therefore proposed the heater of the electrically heatable catalyst (E-catalyst) to supply energy via a capacitor. The condenser can be separated from the heating device by a circuit breaker and via a DC / DC converter connected to the vehicle battery. Did he Capacitor reaches a sufficiently high charging voltage, the switch will  closed and the capacitor discharges through the heater of the E- Catalyst, whereby it is heated.

By using a capacitor as an energy store for the heating device device of the e-catalyst can shorten the response time of the e-catalyst again and thus a faster conversion can be achieved by the e-catalyst.

The use of a MOS field-effect transistor is used as the circuit breaker known. However, MOS field effect transistors have the disadvantage that they have one have relatively high internal resistance (approx. 5 mΩ) and are also very expensive.

The present invention has for its object an improved arrangement propose to heat an electrically heated catalyst, which on the one hand, it can be built up easily and cheaply, and on the other hand reaching the activation temperature of the catalyst as quickly as possible guaranteed to ensure high quality exhaust gas cleaning.

This object is achieved according to the present invention by an arrangement with solved the features of claim 1. The subclaims define preferred ones and advantageous embodiments of the present invention.

According to the invention, a capacitor or a capacitor circuit is also used as Energy storage for heating the heating device of the electrically heated Kata lysators (e-catalyst) used. The capacitor circuit is connected via a controllable switch either connected to or from the heater Cut.

The capacitor circuit is to be dimensioned such that it is open Switch is charged to a nominal voltage of 15 V-50 V and at closed switch within the first 3 s at least 75% of the previous releases stored energy to the e-catalyst.

A relay is preferably used as the switching element.  

A relay has the advantage that its purchase costs are relatively low and it also has a very low internal resistance (in the order of 0.5 Ω) having. However, relays generally have the disadvantage that a Closing the relay at high voltages is possible while opening the Relay already leads to the generation of an arc at voltages above approx. 18 V, what a quick burn of the contact points of the relay and thus one rapid wear.

The previously described problems associated with the use of a relay are, however, are not significant in the context of the present invention, since the present invention on the use of a previously described Capacitor circuit based as an energy store for the heating device. This means that the relay is only opened when the Capacitor circuit has already discharged to a certain extent, so that a Opening the relay at high voltages is prevented. On the other hand, it will Relay when a relatively high charging voltage of the capacitor circuit is present closed to heat the e-catalyst, but what - as before has been explained - in contrast to the opening case is unproblematic.

In this way, an arrangement for heating a electrically heated catalyst created, which is cheap and simple Means can be produced and also by using a capacitor circuit as an energy store for the heating device of the electrically heated catalyst a very fast reaching the activation temperature of the catalyst and thus ensures a quick conversion and high quality exhaust gas cleaning.

The current state of charge of the capacitor circuit is advantageous monitored to deactivate the charging process when an overload is detected can. Is the capacitor circuit made up of several (connected in series) Capacitor cells built up, each one of these capacitor rows monitored and bridged if an overload is detected.

Measurements have shown that it is used to heat the catalyst and the course of the conversion is particularly advantageous if the  Capacitor circuit is charged with the relay open so that at Closing the relay delivers an energy in the order of 10 kWs and 30 kWs is possible. A heating energy of preferably about 15 kWs can can be achieved, for example, if the capacitor circuit, which is a Has a total capacity of approx. 19F when the relay is open Nominal voltage of approx. 40 V is charged.

The invention is described below with reference to the drawing preferred embodiment described.

Fig. 1 shows the construction of an arrangement for the electrical heating of a catalyst according to a preferred embodiment of the present invention,

Fig. 2 shows a catalyst system consisting of an electrically heated catalyst, a support catalyst and a three-way catalyst,

Fig. 3 shows the course of the ideally required for heating the electrically heated catalyst performance to the advantageous effect to explain a capacitor as an energy storage for heating the catalyst, and

FIG. 4 shows the conversion rates and HC emissions at various measuring points shown in FIG. 2 using the present invention.

Before discussing in the manner shown in Fig. 1 assembly 2 are first with reference to the illustrations of FIG. To FIG. 4, the achievable by the use of a capacitor as an energy storage advantages will be explained in more detail.

As has already been mentioned at the beginning, the heating of the electrically heated catalyst (e-catalyst) sought. An optimal one The solution would consist in the first second after commissioning the To guide the catalyst into the catalyst, which power to heat on the one hand the metal sheets of the e-catalytic converter and on the other hand the (at one  Cold start) relatively cold exhaust gas from 20 ° C to 300 ° C is required. In the Subsequent seconds would then only have that energy or power are supplied, which for heating the exhaust gas mass flow from its current temperature to 300 ° C is required. Does the exhaust gas temperature have values reached above 300 ° C, the external heating can possibly be switched off.

If it is assumed that the metal plate of the e-catalyst to be heated weighs approx. 50 g, an energy of approx. 7 kWs is required for a sudden heating to 300 ° C. If it is further assumed that the exhaust gas mass flow has a constant temporal composition, the exemplary power requirement shown in the following table results for a period of 10 s after switching on the internal combustion engine of the motor vehicle:

In Fig. 3 the variation of the sum and for heating the exhaust air (fourth column of the table) was applied (fifth column of the table) from the (third column of the table) for heating the E-catalyst in the form of the curve (a). For comparison, the characteristic curve (b) of the power that can be output by a capacitor with a nominal voltage of 40 V and a capacity of 19 F is also plotted in FIG. 3 if it is assumed that this corresponds to the internal resistance of a conventional e-catalytic converter 0.1 Ω resistor discharges.

It can be seen from the illustration in FIG. 3 that the theoretically calculated power requirement can be approximated quite well by the discharge function of an appropriately dimensioned capacitor. In the example shown in FIG. 3, the capacitor is dimensioned in particular in such a way that an energy of approximately 15 kW can be emitted by it with a nominal charge of 40 V, the energy emitted by the capacitor changing as the discharge process progresses in accordance with FIG Fig. 3 reduced discharge function and finally (at about 9 s) has reached the value 0 kWs. At least 75% of the energy stored by the capacitor is released within the first three seconds, so that the e-catalyst is heated as quickly as possible.

FIG. 2 shows the construction of a catalytic converter close to the engine, consisting of an e-catalytic converter 8 heated via a condenser, a support catalytic converter 9 and a three-way catalytic converter 10 . The exhaust gas flow is fed to the e-catalytic converter 8 via the exhaust pipe of a motor vehicle in the direction of the arrow, at the measuring points M1, M2 and M3 shown in FIG. 2, ie at the input of the e-catalytic converter 8 , at the outlet of the e-catalytic converter 8 and at Output of the support catalyst 9 , temperature and pollutant measurements have been made and it is assumed that the e-catalyst 8 is heated by the energy emitted by a charged capacitor with a capacity of 19F and a nominal voltage of 40V. In the fully charged state of the capacitor, the capacitor 8 is supplied with an energy of approximately 15 kWs by the capacitor.

FIG. 4A shows the course of the exhaust gas temperature over time at the measuring points shown in FIG. 2, wherein it can be seen that the exhaust gas temperature at the outlet of the e-catalyst 8 (curve (b)) rises quickly and slightly again after approx. 2 s drops, but remains above 300 ° C. Curve (a) corresponds to the exhaust gas temperature at measuring point M1 shown in FIG. 2, while curve (c) is assigned to the exhaust gas temperature at measuring point M3.

The course of curve (b) can be dependent on the selected charging parameters can be varied. When the nominal charge of the capacitor is increased, it gets steeper Rise, while increasing the capacitance of the capacitor Maximum temperature can be kept longer.

. The course of the HC emissions (c) applied to the shown in Figure 2 measuring points M1-M3 and the resulting conversion rate (curve (d)) E catalyst - in Figure 4B with the curves (a).. It can be seen from the illustration in FIG. 4B that the conversion starts after about 0.5 s. The cumulative HC emission during the measurement period of 10 s is only approx. 0.023 g. For comparison, without electrical heating, a conversion after approx. 6 s with a cumulative HC emission of 0.065 g and with heating with the help of a battery with a comparable power output is only after about 1.5 s a conversion with a cumulative HC emission of 0.029 g achievable. This comparison makes it clear that very effective catalyst heating with low pollutant emissions can be achieved by using a condenser. Other advantages of using a capacitor compared to battery heating are the low weight and the small construction volume as well as the long service life. Furthermore, the motor of the respective motor vehicle is not loaded when a capacitor is used.

In Fig. 1 illustrates an arrangement for the electrical heating of a catalyst according to a preferred embodiment of the present invention. A capacitor circuit 5 is charged via a DC / DC converter 4 from the vehicle battery 3 of the corresponding motor vehicle when a relay 6 used as a controllable switch is open. This is automatically triggered by a control unit 7, for example, when the internal combustion engine of the motor vehicle is at a standstill, since when the internal combustion engine is started later, electrical heating of the e-catalyst provided with the reference numeral 8 in FIG. 1 or its heating device is possible via the charging energy of the capacitor circuit 5 should be. Furthermore, a generator 2 is shown in FIG. 1, which serves as an energy supply for the vehicle electrical system 1 or the consumers connected to it, and for charging the vehicle battery 3 .

The DC / DC converter 4 can be designed for a power of 100 W, for example. The vehicle battery 3 delivers a voltage of z. B. 12 V. With this data, a charging of the capacitor circuit or capacitor battery 5 to a nominal voltage of 15 to 50 V, preferably to the previously assumed 40 V, is possible. The capacitor circuit 5 could preferably be dimensioned such that it is charged to a nominal voltage of 15 V-10 V when the switch is open and releases at least 75% of the previously stored energy to the e-catalyst within the first 3 s when the switch is closed (see FIG . 3).

The control unit 7 monitors the starting or starting of the internal combustion engine. Immediately after starting, the control unit 7 closes the relay 6 , so that the heating device of the e-catalytic converter can be heated by the energy emitted by the previously charged capacitor circuit 5 . The relay 6 serving as a circuit breaker is designed, for example, for a short-term maximum current of approximately 350 A. During the discharge of the capacitor circuit 5 , the current flowing through the relay drops rapidly, so that the relay can be opened again after a short time without voltage or current. For this purpose, the control unit 7 advantageously monitors the current charging or discharging state of the capacitor circuit 5 and automatically opens the relay 6 when the current charging of the capacitor circuit 5 has reached a certain lower limit value. The capacitor circuit 5 is then available again for a new charging process.

Referring to FIG. 1, the capacitor circuit is formed by a plurality of capacitor cells 5 a- 5 d. The control unit 7 monitors the state of charge of each individual capacitor cell in order to avoid overcharging. If a certain maximum voltage is exceeded, the corresponding capacitor cell is bridged with the aid of a transistor in order to derive the charging current. After the charging process has ended, the DC / DC converter 4 and the charging voltage monitoring of the control unit 7 should be switched off.

Claims (10)

1. Arrangement for the electrical heating of a catalyst, with a Energiever supply unit ( 3 , 4 ), with a capacitor circuit ( 5 ) which is connected to the output of the energy supply unit ( 3 , 4 ), and with a switching device ( 6 ), which between the capacitor circuit ( 5 ) and a heater ( 8 ) of the catalyst is connected, that the capacitor circuit ( 5 ) either for heating with the heater ( 8 ) or for charging the capacitor circuit ( 5 ) by the energy supply unit ( 3 , 4th ) is separated from the heating device ( 8 ), characterized in that the capacitor circuit ( 5 ) and the power supply unit ( 3 , 4 ) are designed such that the capacitor circuit ( 5 ) in the open state of the switching device ( 6 ) to a nominal voltage of 15 V-50 V is charged and in the closed state of the switching device ( 6 ) within the first three seconds at least 75% releases the previously stored energy to the heating device ( 8 ). 2. Arrangement according to claim 1, characterized in that the Schaltvorrich device ( 6 ) comprises a relay as a switching element. 3. Arrangement according to claim 1 or 2, characterized in that the energy supply unit comprises a battery ( 3 ) and a series-connected DC / DC converter ( 4 ). 4. Arrangement according to one of the preceding claims, characterized in that monitoring means ( 7 ) are provided which monitor the capacitor circuit ( 5 ) with regard to possible overcharging and, if an overload is detected, a further charging of the capacitor circuit ( 5 ) by the energy supply unit ( 3 , 4 ) prevent. 5. Arrangement according to claim 4, characterized in that the capacitor circuit ( 5 ) comprises a plurality of individual capacitors connected in series ( 5 a... 5 d), and that the monitoring means ( 7 ) are designed such that they the state of charge of each individual capacitor ( 5 a... 5 d) monitor and if an overcharge of an individual capacitor ( 5 a... 5 d) is detected, bridge it. 6. Arrangement according to one of the preceding claims, characterized in that the capacitor circuit ( 5 ) and the power supply unit ( 3 , 4 ) are designed such that the capacitor circuit ( 5 ) in the open state of the switching device ( 6 ) can be charged to a state of charge which, when the relay ( 6 ) is closed, enables energy to be delivered to the heating device ( 8 ) of the catalytic converter between 10 kWs and 30 kWs. 7. An arrangement according to claim 6, characterized in that the capacitor circuit (5) and the power supply unit (3, 4) are designed such that the capacitor circuit (5) in the open state of the switching device (6) can be charged to a state of charge With the relay ( 6 ) closed, an energy output of approx. 15 kWs to the heating device ( 8 ) of the catalytic converter is made possible. 8. Arrangement according to claim 6 or 7, characterized in that the Kon capacitor circuit ( 5 ) and the power supply unit ( 3 , 4 ) are designed so that the capacitor circuit ( 5 ) in the open state of the Schaltvor direction ( 6 ) to a nominal voltage can be charged by 40 V. 9. An arrangement according to any one of the preceding claims, characterized net gekennzeich that the switching device (6) is driven by a control unit (7) which is designed such that it automatically, the switching device (6) lysators to start up the Kata closes. 10. Use of an arrangement according to claim 9 in a motor vehicle which is driven by a motor, characterized in that the control unit ( 7 ) is designed such that it closes the switching device ( 6 ) automatically when starting the engine and the switching device ( 6 ) opens again when the charge stored after closing the switching device ( 6 ) by the capacitor circuit ( 5 ) has dropped to a predetermined lower limit.