WO2021259765A1

WO2021259765A1 - Method and device for operating an electric heater of a catalytic converter

Info

Publication number: WO2021259765A1
Application number: PCT/EP2021/066471
Authority: WO
Inventors: Tino Arlt; Adrian-Val HAREA
Original assignee: Vitesco Technologies GmbH
Priority date: 2020-06-24
Filing date: 2021-06-17
Publication date: 2021-12-30
Also published as: DE102020207872B4; CN115885094A; DE102020207872A1; KR20230003309A

Abstract

The invention relates to a method for operating an electric heater (4) of a catalytic converter (3), wherein the heater (4) is connected via a controllable switch (12) to an energy source (5) which supplies an output voltage which is specified by a voltage range (II; IV) which extends from a minimum voltage value to a maximum voltage value but which can also assume voltages outside of said voltage range (II; IV), wherein a control unit (6) detects the output voltage and based on a difference value between the detected output voltage and a predefined reference voltage, controls the controllable switch (12) in an opening and closing manner with pulse-width modulation with a pulse duty factor, and the control unit (6) controls the controllable switch (12) with pulse-width modulation with a pulse duty factor which is adapted such that a heating power of the electric heater (4) corresponds to a predefined nominal heating power.

Description

description

Method and device for operating an electrical heater for a catalytic converter

The invention relates to a method and a device for operating an electrical heater of a catalytic converter, the heater being connected via a controllable switch to an energy source providing an output voltage, which output voltage is specified over a voltage range ranging from a minimum voltage value to a maximum voltage value, but also voltages outside this voltage range, wherein a control unit detects the output voltage and controls the controllable switch to open or close depending on a difference value between the detected output voltage and a predetermined reference voltage value.

Such a method and such a device are known from DE 196 45 016 C1. There it is stated that for a particularly low emission of pollutants, especially when restarting an internal combustion engine, it is necessary for the catalytic converter to be quickly heated to its operating temperature. For this purpose, for example, an electrical heating device should be provided which electrically heats the catalytic converter. A corresponding electrical heating device for a catalytic converter is, for example, from "The system development of the electrically heatable catalytic converter", Erhard Otto et al. , Motortechnische Zeitschrift 56 (1995) 9, page 488 ff. The power supply of the electrically heated catalytic converter is a particular problem area, as it has serious repercussions on the vehicle electrical system and engine operation.

In the method there, the voltage is measured as a reference voltage at the start of the heating of the catalytic converter, the voltage being continuously determined as the current voltage and compared with the reference voltage while the catalytic converter is being heated. The heating of the catalytic converter is canceled if the difference between the reference voltage and the current voltage is greater than a difference value. In this way, due to the voltage drop during heating, the quality of the voltage source is determined and, depending on the quality, heating is interrupted or continued. However, this only addresses the problem that the energy source is not overburdened by the heating.

Furthermore, document DE 10 2018 120 402 A1 discloses a method and devices for controlling an electrically heated catalytic converter system of a vehicle, it being determined depending on a power requirement whether a high-voltage network or a low-voltage network is to be used to heat the catalytic converter system.

An electrically heated catalytic converter is mainly used to accelerate catalytic converter heating after a cold engine start. It can also be used to reheat a catalytic converter that has cooled down during a drive cycle. Electrically heated catalytic converters are currently designed to work at a nominal voltage of a voltage supply of, for example, 12 V or 48 V, with a required heating power of, for example, 2.5 kW or 4 kW being common. The electrically heated catalytic converter is usually designed in such a way that it achieves the required heating power at the nominal voltage. Deviations from these nominal values are often used to investigate the effects and advantages of an electrically heated catalyst during the development phase.

The power supply in motor vehicles is mostly carried out with the help of batteries with output voltages of, for example, 12 or 48 V, whereby these are only the nominal voltages, but considerable deviations from this can occur during operation, as these batteries can be subject to heavy loads due to a high number of consumers that have to be operated at the same time . In addition, these batteries can be charged to voltages higher than their nominal voltage. For example, the operating voltage range of a 12 V battery is set between approximately 9 V and 14 V, while it is defined between 36 V and 52 V for a 48 V battery. This means that the batteries may be loaded by connecting consumers if their current voltage is within these ranges.

A typical requirement is that the specified heating power of, for example, 4 kW of the electrically heated catalytic converter should be available over the entire permitted voltage range of, for example, 36 V to 52 V of a 48 V battery. The electrically heated catalytic converter has a purely resistive characteristic. This means that the desired nominal heating output can only be achieved with the Nominal voltage is generated. If the voltage is lower, the heating output will also be lower, which means that the warm-up phase of the catalytic converter is significantly longer. If the battery voltage was higher than the nominal voltage, the heating output would be correspondingly greater, which would accelerate the heating of the catalytic converter. This relationship is illustrated in FIG. 2, which shows the quadratic dependence of the heating power on the battery voltage. It can be seen that the actual heating output can have considerable deviations within the permitted voltage range.

The object of the invention is to specify a method and a device for operating an electrical heater for a catalytic converter, in which a constant heating power is made possible over the entire specified output voltage range of an energy store.

The object is achieved by a method for operating an electrical heater for a catalytic converter, the electrical heater being connected via a controllable switch to an energy source providing an output voltage, which output voltage is specified over a voltage range ranging from a minimum voltage value to a maximum voltage value, but also voltages outside of this voltage range, and wherein a control unit detects the output voltage and, depending on a difference value between the detected output voltage and a predetermined reference voltage value, controls the controllable switch in a pulse-width-modulated manner with a pulse-width-modulated opening and closing ratio, in which, in the case of a positive difference between the output voltage and the reference voltage value, the control unit controls the controllable switch in a pulse-width-modulated manner with a duty cycle adapted in such a way that the output of the electrical heater is a predetermined value n corresponds to the nominal heating output.

A pulse-width-modulated control signal is characterized in that a change between switched-off and switched-on operating phases is specified, the duration of the respective on and off phase or the ratio between on and off phases being referred to as the duty cycle and an average power above the Time results and can be varied as required. With an increasing proportion of the on-phases, one speaks of an increasing pulse duty factor, so a pulse duty factor of 100% corresponds, as it were, to a permanent switched-on state. One embodiment of the invention is characterized in that as the difference value between the output voltage and the reference voltage value decreases, the duty cycle of the pulse width modulation of the control signal of the controllable switch increases. In this case, a decreasing differential value means a decreasing output voltage of the energy source. In order to be able to maintain the nominal heating power when the output voltage of the energy source decreases, the proportion of the one-phase pulse width modulation, i.e. the pulse duty factor, must be increased. By adapting the pulse duty factor as a function of the difference value between the output voltage and the reference voltage value, i.e. ultimately the level of the output voltage, the nominal heating power can advantageously be kept constant at least over a predefined voltage range.

In a further embodiment of the invention, the nominal heating power is achieved when the duty cycle of the pulse width modulation of the control signal of the controllable switch is 100% and the difference between the output voltage and the reference voltage value assumes the value 0. In other words, when the output voltage reaches the lower limit specified by the reference value, the maximum, i.e. 100%, is exhausted by the duty cycle in order to maintain the nominal heating output. This enables, in a simple, advantageous manner, the mutual coordination of the work or load areas of the electrical heater and the energy source.

In continuation of the idea, in a further embodiment of the invention, the predefined reference voltage value is established in such a way that it corresponds to the minimum voltage value of the energy source. In this way, the entire specification range of the output voltage of the energy source can be used in an advantageous manner and it can be ensured that the nominal heating power can still be achieved even at the lower end of the specification range of the energy source.

Another embodiment of the subject matter according to the invention is characterized in that the pulse duty factor of the pulse width modulation of the control signal is approximately 50% when the output voltage corresponds to the maximum voltage value of the energy source. The definition of a value of 50% for the duty cycle of the pulse width modulation at the upper one The specification limit ensures that in the event of an overvoltage of the energy source, overheating of the electrical heater and thus damage to the system through the possibility of further reducing the pulse duty factor can be avoided.

Furthermore, an embodiment of the invention can be determined in that the minimum voltage value of the energy source is 9V or 36V and that the maximum voltage value of the energy source is 14V or 52V and that the nominal heating power of the electric heater is set at 2.5kW or 4kW. With these values, reference is made to two established designs of on-board electrical systems of motor vehicles, in which the method according to the invention can advantageously be used. On the one hand, reference is made to a 12V on-board network system, where the specified working range of the energy source is between 9V and 14V and the nominal heating power is only 2.5 kW due to the lower voltage. On the other hand, reference is made to a 48V on-board network system, whereby the specified working range of the energy source is between 36V and 52V and the nominal heating output can be designed to a value of 4 kW due to the higher voltage.

The invention also relates to a device for operating an electrical heater for a catalytic converter, with a controllable switch that connects the electrical heater to an energy source providing an output voltage, which output voltage is specified over a voltage range ranging from a minimum voltage value to a maximum voltage value, but also voltages outside this voltage range, and with a control unit that is set up to detect the output voltage and, depending on a difference value of the detected output voltage to a predetermined reference voltage value, to open and close the controllable switch in a pulse-width modulated manner with a duty cycle, the control unit also being set up to do so to carry out a method according to one of the aforementioned embodiments.

In a further embodiment of the device, the switch is part of a DC-DC converter. This enables an integrated, inexpensive design of the device. The DC-DC converter can be designed as a step-down converter.

The invention thus relates to a method and a device to increase the heating power of the electrically heated catalytic converter over a permitted voltage range to stabilize a voltage supply at a nominal heating power.

For this purpose, in one embodiment, for example, the required nominal heating output of the electrical heating of the catalytic converter is no longer based on the nominal voltage of the energy source, but on the minimum permissible voltage of the energy source or power supply and then by pulse width modulation of the control signal for the switch that controls the electrical heating connects to the battery, the heating power is regulated at higher output voltages of the energy source by adjusting the duty cycle of the pulse width modulation to the nominal heating power. This means that with higher output voltages of the energy source, a lower pulse duty factor of the control signal for the switch is required in order to set the required nominal heating power.

This is illustrated in FIG. 3. There a permissible voltage range of 36 to 52 V is specified, whereby the nominal heating power of 4 kW should be achieved with a reference voltage of 36 V, which at the same time represents the minimum voltage of the specified working range of the energy source. In order to maintain this heating output of 4 kW over the entire voltage range between 36 V and 52 V, i.e. not to generate increased heating output with a higher output voltage of the energy source, the duty cycle of the pulse width modulation of the control signal for the switch that connects the energy source or battery to the electrical Heating of the catalytic converter connects continuously from 100% at 36 V to around 50% when the specified maximum value of the output voltage of the energy source at 52 V is reached.

This advantageous control of the heating output enables constant compliance with the nominal heating output over the entire permissible specified voltage range of the energy source. Both slow and fast voltage changes, which are influenced, for example, by the battery technology and the voltage network or the consumers connected to it, can thus be compensated for by the fast reaction and regulation of the pulse width modulation. In addition, the catalytic converter heating is not exposed to any unpredictable fluctuations in each driving cycle and over the entire specified range of the output voltage of the energy source or battery voltage, but rather remains constant in a calculable manner. In one embodiment of the device according to the invention, the switch can be part of a DC-DC converter, the DC-DC converter then preferably being designed as a step-down converter.

The method and the device can advantageously be used both for gasoline-powered and diesel-powered internal combustion engines, preferably in motor vehicles. The catalytic converter can be attached at any location in the exhaust system.

The invention is to be described in more detail below on the basis of an exemplary embodiment with the aid of figures. Show it

1 shows a basic arrangement of a device according to an embodiment,

2 shows a representation of the voltage and heating power ranges in the case of an unregulated heating control and

3 shows a representation of the voltage and heating power ranges in the case of a heating control regulated according to the invention.

1 shows an internal combustion engine 1 which has an exhaust line 2 in which a catalytic converter 3 is installed. The catalytic converter 3 has an electrical heating device 4 which heats the catalytic converter 3 to a predetermined operating temperature. The heating device 4 is supplied with electrical energy from a voltage source, for example a battery 5 or a capacitor as an energy store. The exemplary embodiment is explained below using a battery 5.

The battery 5 is connected to the heating device 4 with a positive pole via a first supply line 11. The negative pole is also connected to the heating device 4 via a second supply line 12 and a switch 13. The battery can have a nominal voltage of 12 V, i.e. the voltage of a conventional vehicle battery, or a nominal voltage of 48 V. For a vehicle battery with a nominal voltage of 48 V, a permissible voltage range of, for example, 36 V to 52 V is specified. Instead of simply connecting the battery 5 to the heating device 4 via a switch 13, a DC-DC converter which has the switch 13 can also be used.

In a simple embodiment, the heating device 4 has, for example, a resistance wire as a heating element. A control unit 6 is also provided, which is connected to the internal combustion engine 1 via a data bus 8, to the second supply line 12 via a second measuring line 9, to the first supply line 11 via a first measuring line 10 and to the controllable switch 13 via a control line 7 is. The control unit 6 is also connected via a sensor line 15 to a temperature sensor 14 which is arranged on the catalytic converter 3.

The internal combustion engine 1 has an air mass meter 18 which is arranged in the intake duct and measures the air mass drawn in by the internal combustion engine. Furthermore, the internal combustion engine 1 has a cooler 16 which is filled with cooling liquid, which cools the internal combustion engine via cooling ducts which are introduced into the internal combustion engine. In addition, a generator 19 is provided on the internal combustion engine 1, which is driven by the internal combustion engine and charges the battery 5 via a charging line 20.

Depending on parameters of the internal combustion engine 1, the voltage of the battery 5 and the temperature of the catalytic converter 3, the control unit 6 controls the electrical heating device 4 with which the catalytic converter 3 is heated to its predetermined operating temperature.

The temperature of the catalytic converter 3 can be regulated, for example, in that the control device 6 measures the temperature of the catalytic converter 3 when the internal combustion engine 1 is started. The control unit 6 then compares the measured temperature of the catalytic converter 3 with a predetermined catalytic converter temperature stored in the memory 17. The stored catalyst temperature preferably corresponds to the optimum operating temperature of the catalyst of 350 ° C., for example. If the comparison shows that the measured catalytic converter temperature is greater than or equal to the stored catalytic converter temperature, no electrical heating of the catalytic converter is carried out since the catalytic converter 3 is sufficiently warm. Otherwise, the switch 12 is controlled in such a way that the heating device 4 operates with nominal heating power until the catalytic converter has reached operating temperature. FIG. 2 shows the quadratic dependence of the heating power on the applied battery voltage. In the example shown, the battery voltage has a specified output voltage range II of 36 V to 52 V. Due to the resistance of the heater, this results in a heating power range I from 2.25 kW to 4.69 kW. At the nominal voltage of 48 V, the required heating output of 4 kW is achieved. This is shown with a point III.

A curve of the heating power and the duty cycle of a pulse-width-modulated control signal for the switch 12 when using the method according to the invention or using a device according to the invention is shown in FIG. 3. The specified output voltage range IV of the battery voltage is again between 36 V and 52 V. Heating output of 4 kW already at the minimum voltage value used as the reference voltage, this output voltage range IV reaches, which is represented by V. Thereafter, the heating power is regulated to a constant value of 4 kW by a pulse-width-modulated control of the switch 12 of the heating arrangement according to FIG. 1. For this purpose, the pulse duty factor of the pulse-width-modulated control signal must be set as a function of the determined current value of the battery voltage. The dependence of the pulse duty factor on the battery voltage is shown with a curve VII. As can be seen in FIG. 3, at the point of the minimum voltage of the output voltage range IV, the duty cycle of the pulse width modulation (PWM) is 100% and decreases with increasing battery voltage such that the heating power is kept constant at 4 kW.

Claims

1 . A method for operating an electrical heater (4) of a catalytic converter (3), the electrical heater (4) being connected via a controllable switch (12) to an energy source (5) providing an output voltage, which output voltage varies from a minimum voltage value to a Maximum voltage value reaching voltage range (II; IV) is specified, but can also accept voltages outside this voltage range (II; IV), whereby a control unit (6) detects the output voltage and depending on a difference value of the detected output voltage to a predetermined reference voltage value, the controllable switch ( 12) pulse width modulated with a duty cycle controls opening and closing, characterized in that with a positive difference value of the output voltage to the reference voltage value, the control unit (6) controls the controllable switch (12) pulse width modulated with a duty cycle adjusted in such a way that a heating power of the electric heater (4) corresponds to a predetermined nominal heating power.

2. The method according to claim 1, characterized in that as the difference value between the output voltage and the reference voltage value decreases, the pulse duty factor of the pulse width modulation of the control signal of the controllable switch (12) increases.

3. The method according to claim 1 or 2, characterized in that the nominal heating power is achieved when the duty cycle of the pulse width modulation of the control signal of the controllable switch (12) is 100% and the difference value of the output voltage to the reference voltage value assumes the value 0.

4. The method according to any one of claims 1 to 3, characterized in that the predetermined reference voltage value corresponds to the minimum voltage value of the energy source (5).

5. The method according to any one of claims 1 to 4, characterized in that the duty cycle of the pulse width modulation of the control signal is around 50% when the output voltage corresponds to the maximum voltage value of the energy source (5).

6. The method according to any one of claims 1 to 5, characterized in that the minimum voltage value of the energy source (5) is 9V or 36V and that the maximum voltage value of the energy source (5) is 14V or 52V and that the nominal heating power of the electric heater is set to 2, 5kW or 4kW is specified.

7. Device for operating an electric heater (4) of a catalytic converter (3), with a controllable switch (12) which connects the electric heater (4) to an energy source (5) which provides an output voltage and which has an output voltage above a minimum voltage value to a maximum voltage value reaching voltage range (II; IV) is specified, but can also accept voltages outside this voltage range (II; IV), with a control unit (6) which is set up to detect the output voltage and dependent on a difference value of the detected output voltage to control the controllable switch (12) with a pulse width modulated opening and closing at a predetermined reference voltage value with a pulse duty factor, characterized in that the control unit (6) is also set up to carry out a method according to one of claims 1 to 6.

8. The device according to claim 7, wherein the switch 13 is part of a DC-DC converter.

9. The apparatus of claim 8, wherein the DC-DC converter is a buck converter.