CN111894703A

CN111894703A - System for unfreezing exhaust gas treatment fluid of engine and liquid level monitoring method

Info

Publication number: CN111894703A
Application number: CN201910370947.4A
Authority: CN
Inventors: 刘毅
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2019-05-06
Filing date: 2019-05-06
Publication date: 2020-11-06
Also published as: DE102020204518A1

Abstract

Disclosed are a system for thawing an exhaust treatment fluid of an engine and a fluid level monitoring method, the system comprising: an exhaust gas treatment liquid container (100) for storing an exhaust gas treatment liquid; a PTC electric heater (20) provided in the exhaust gas treatment liquid container (100), the PTC electric heater (20) having a heating surface that generates heat after being activated; a current sensor that measures an operating current of the PTC electric heater (20); and an electronic control unit receiving a signal from the current sensor and controlling an operation of the PTC electric heater, wherein the electronic control unit is configured to instruct the current sensor to measure an operating current of the PTC electric heater after the PTC electric heater is started; and generating an early warning signal after N measurements of the current sensor indicate that each measured operating current value is less than a predetermined current value (Ip), wherein N is an integer greater than 1.

Description

System for unfreezing exhaust gas treatment fluid of engine and liquid level monitoring method

Technical Field

The present application relates to a system for thawing an exhaust treatment fluid of an engine, in particular a diesel engine, and a method of monitoring the fluid level during the thawing process.

Background

As environmental regulations become more stringent, it is common for motor vehicles, particularly diesel vehicles, to incorporate exhaust treatment systems to reduce the amount of off-spec material emitted from the exhaust of the engine, particularly diesel engines. The exhaust gas treatment system includes an exhaust treatment fluid container and a selective catalytic reduction device connected to the exhaust treatment fluid container and having a nozzle opening into an exhaust pipe of the motor vehicle. According to the requirement, an exhaust treatment fluid such as urea aqueous solution can be supplied from an exhaust treatment fluid container to a nozzle of the selective catalytic reduction device and injected into an exhaust pipe by the nozzle so as to be mixed with the engine exhaust gas for reaction and reduce the content of nitrogen oxides in the exhaust gas.

It can be seen that the exhaust gas treatment liquid is a consumable product and needs to be replenished on time after the motor vehicle travels for a certain distance to ensure that the reaction of the selective catalytic reduction device can be performed as required, thereby reducing the content of nitrogen oxides in the exhaust gas. Therefore, a liquid level sensor is usually disposed in the exhaust treatment fluid container, and when the liquid level of the exhaust treatment fluid in the exhaust treatment fluid container is lower than a predetermined value, a warning can be given to a driver of the motor vehicle to remind that the exhaust treatment fluid should be filled.

However, in cold winter seasons, particularly for northern areas, exhaust treatment fluids such as aqueous urea solutions freeze in their containers after the motor vehicle has been parked for a long time, because the air temperature is often below zero. In order to thaw the exhaust gas treatment liquid, an electric heater is further provided in the exhaust gas treatment liquid container, which generates heat when energized so as to melt the frozen exhaust gas treatment liquid in the exhaust gas treatment liquid container, and can be supplied to the nozzle of the selective catalytic reduction device as needed.

Such electric heaters are often disposed at the bottom of the exhaust treatment fluid container and near the outlet of the exhaust treatment fluid container. When the relatively full exhaust gas treatment liquid container is frozen, the electric heater needs to be energized to dissipate heat from the heating surface of the electric heater to the periphery in order to thaw the container. Then, the solid exhaust gas treatment liquid around the heating surface of the electric heater is converted into a liquid exhaust gas treatment liquid and discharged from the exhaust gas treatment liquid container via the outlet. At this time, the periphery of the electric heater is isolated from other frozen solid exhaust treatment fluid by air. Because air is a poor conductor of heat, the heat of the electric heater will be difficult to transfer further to other frozen solid exhaust treatment fluids, resulting in an inability to further thaw them. In this case, the level sensor has failed to function and issues a warning that the liquid exhaust gas treatment fluid is insufficient, so that the driver is not aware at all that the liquid exhaust gas treatment fluid has not been discharged and the exhaust emissions of the motor vehicle exceed the standard.

Disclosure of Invention

The invention aims to solve the problem that the shortage of liquid waste gas treatment liquid cannot be timely known due to insufficient unfreezing degree when the waste gas treatment liquid is unfrozen.

According to one aspect of the present application, there is provided a system for defrosting an exhaust treatment fluid, in particular an aqueous urea solution, of an engine, in particular a diesel engine, comprising:

an exhaust gas treatment liquid container for storing an exhaust gas treatment liquid;

a PTC electric heater provided in the exhaust gas treatment liquid container, the PTC electric heater having a heating surface that generates heat after being started;

a current sensor for measuring the operating current of the PTC electric heater; and

an electronic control unit receiving a signal from the current sensor and controlling the operation of the PTC electric heater, wherein the electronic control unit is configured to instruct the current sensor to measure an operating current of the PTC electric heater after the PTC electric heater is started; and generating an early warning signal after the N times of measurement results of the current sensor indicate that the measured working current value is less than a preset current value each time, wherein N is an integer greater than 1. Whether the waste gas treatment liquid in the waste gas treatment liquid container is insufficient or not is predicted by adopting the working current measurement result of the PTC electric heater, so that the liquid level condition in the current waste gas treatment liquid container when unfreezing is carried out can be more accurately known, and the excessive discharge is avoided. In addition, whether the liquid level is insufficient or not is judged according to the current measurement result of the PTC current sensor, and the utilization rate of the waste gas treatment liquid can be correspondingly improved.

Optionally, the N times of measurement results are results obtained by the current sensor continuously measuring the operating current of the PTC electric heater.

Optionally, each measurement result is processed by signal filtering, in particular by high-frequency signal filtering, before being compared with a predetermined current value. The clutter interference can be effectively reduced by filtering the measurement result.

Optionally, the current sensor is integrated within the PTC electric heater. The technical scheme of the application can be conveniently implemented by software upgrading without changing the hardware design of the existing system by utilizing the current sensor integrated in the PTC electric heater.

Alternatively, the predetermined current value is determined according to a coverage rate of the heating surface of the PTC electric heater covered with the liquid exhaust gas treatment liquid. In this way, the designer can determine the early warning strategy for (winter) air temperature characteristics and/or specific shapes of the exhaust treatment fluid containers for different dimensional regions.

Optionally, the system further comprises a liquid level sensor disposed within the exhaust treatment fluid container. The level sensor is arranged to complement the current sensor measurement.

Optionally, the predetermined current value is an operating current value flowing through the PTC electric heater when the coverage of the heating surface of the PTC electric heater reaches 30%.

According to another aspect of the present application, there is also provided a method for monitoring a liquid level when an exhaust gas treatment fluid, in particular an aqueous urea solution, of an engine, in particular a diesel engine, is thawed, wherein the exhaust gas treatment fluid is contained in an exhaust gas treatment fluid container of an exhaust gas treatment system of a motor vehicle, in which exhaust gas treatment fluid container a PTC electric heater is arranged, the method comprising:

measuring the working current of the PTC electric heater after the PTC electric heater is started to heat the waste gas treatment liquid;

and generating an early warning signal after N times of measurement results show that the measured working current value is less than a preset current value each time, wherein N is an integer greater than 1.

Optionally, the N times of measurement results are results obtained by continuing the operating current of the PTC electric heater; and/or each measurement is signal-filtered, in particular high-frequency, before being compared with a predetermined current value.

Alternatively, the predetermined current value is determined according to a coverage rate of the heating surface of the PTC electric heater by the liquid exhaust gas treatment liquid, and particularly the predetermined current value is an operating current value flowing through the PTC electric heater when the coverage rate of the heating surface of the PTC electric heater reaches 30%.

By adopting the technical means, the current liquid level in the waste gas treatment liquid container can be more accurately determined when the waste gas treatment liquid is unfrozen, and the volume of the waste gas treatment liquid available in the waste gas treatment liquid container before early warning is given out is increased.

Drawings

The foregoing and other aspects of the present application will be more fully understood from the following detailed description, taken together with the following drawings. It is noted that the drawings may not be to scale for clarity of illustration and will not detract from the understanding of the present application. In the drawings:

FIG. 1 schematically illustrates a simplified block diagram of an exhaust treatment system;

FIG. 2a schematically illustrates an exhaust treatment fluid in an exhaust treatment fluid container at an initial stage of thawing;

FIG. 2b schematically illustrates the exhaust treatment fluid within the exhaust treatment fluid container after thawing for a period of time and after the liquid exhaust treatment fluid has been discharged;

FIG. 3 schematically illustrates a flow diagram of a method for monitoring a liquid level when an exhaust treatment fluid of an engine thaws according to an embodiment of the present application; and is

Fig. 4 schematically shows a graph of the current flowing through the PTC electric heater measured when the coverage of the heating surfaces of the PTC electric heater with the exhaust gas treatment liquid is different.

Detailed Description

In the various figures of the present application, features that are structurally identical or functionally similar are denoted by the same reference numerals.

FIG. 1 schematically illustrates a schematic of a portion of an exhaust treatment system that may be used for engine exhaust treatment of a motor vehicle. Depending on the context of the application, the motor vehicle may be a diesel vehicle and the engine may thus be a diesel engine. The exhaust treatment system includes an exhaust treatment fluid reservoir 100, a pump module 200 in fluid communication with the exhaust treatment fluid reservoir 100, and a nozzle 300 in fluid communication with the pump module 200. An exhaust treatment fluid, such as an aqueous urea solution, is contained within the vessel 100. The nozzle 300 can extend at least partially into the exhaust gas duct of the diesel vehicle so that, upon actuation of the pump module 200, the exhaust treatment fluid can be supplied under pressure from the vessel 100 to the nozzle 300 and injected into the exhaust gas duct as required to chemically react with the engine exhaust.

In order to monitor whether the exhaust treatment fluid in the vessel 100 is sufficient, a fluid level sensor 10 is typically provided in the exhaust treatment fluid vessel 100. In addition, an electric heater 20 is also provided in the exhaust treatment fluid container 100, generally near the bottom outlet of the interior of the exhaust treatment fluid container 100. Optionally, a filter (not shown) is further provided at the outlet so that the exhaust treatment fluid exiting the vessel 100 is filtered beforehand.

Fig. 2a and 2b schematically show the exhaust gas treatment liquid in the exhaust gas treatment liquid container after a certain period of time from the initial thawing stage and the thawing stage, respectively. For example, in the north in winter, when the vehicle is parked outside for a long time, the exhaust gas treatment fluid in the container 100 is completely frozen and the exhaust gas treatment fluid is in a solid state 30. As can be seen from fig. 2a, for thawing, the electric heater 20 is energized so that heat is dissipated around the electric heater 20. Thus, the exhaust gas treatment liquid around the electric heater 20 will be in the liquid state 31 first. Then, the liquid exhaust gas treatment liquid 31 continuously transfers heat from the electric heater 20 to the surrounding solid exhaust gas treatment liquid 30 as a heat transfer medium.

To prevent engine exhaust from exceeding the standard if the engine is started before all the solid exhaust treatment fluid in the container 100 is completely melted, the electronic control unit of the exhaust treatment system instructs the pump module 200 to operate to discharge the exhaust treatment fluid 31 in a liquid state from the container 100. Therefore, as shown in fig. 2b, when the previously melted exhaust gas treatment liquid 31 is gradually removed or even completely emptied, a space is left between the periphery of the electric heater 20 and the remaining solid exhaust gas treatment liquid 30. That is, only air 40 will remain between the remaining solid exhaust-gas treatment liquid 30 and the electric heater 20. The heat transfer performance of the air 40 is poor compared to the exhaust gas treatment fluid. This makes it difficult to efficiently transfer the heat emitted from the electric heater 20 to the solid exhaust treatment fluid 30, which further increases the tendency of freeze-thaw delay. Furthermore, even damage to the electric heater may be caused by no liquid exchanging heat with the electric heater 20 in time.

In the case where the liquid exhaust treatment fluid 31 is empty, the driver needs to be reminded to fill the exhaust treatment fluid in time. However, sometimes the remaining exhaust treatment fluid is in a frozen solid state and the level sensor 10 is not functional at all. In addition, in order to avoid "dry burning" of the electric heater 20, the liquid level sensor 10 is usually set to a liquid level higher than the entire heating surface of the electric heater 20, which needs to be warned. The level at which an alarm is required means that the driver is alerted as soon as the liquid exhaust treatment liquid is below this level. Thereby reducing the volume of exhaust treatment fluid that can be used before each refill of exhaust treatment fluid.

According to one embodiment of the present application, the electric heater 20 is a PTC (positive temperature coefficient) heater, which mainly includes a heating surface formed of a PTC heating element. A characteristic of PTC electric heaters is that as the temperature of the heating surface increases, the resistance of the PTC electric heater/heater body increases significantly. Therefore, in the case where a PTC electric heater is used as the heater in the exhaust gas treatment liquid container 100, the liquid condition in the exhaust gas treatment liquid container 100 can be determined by monitoring the current flowing through the PTC electric heater.

FIG. 3 schematically illustrates a flow chart of a method for monitoring a liquid level when an exhaust treatment fluid of an engine thaws according to one embodiment of the present application. For example, with this method, it is monitored during the thawing of the exhaust treatment fluid whether the exhaust treatment fluid in the exhaust treatment fluid container 100 is sufficient to issue a warning of refilling of the exhaust treatment fluid in a timely manner. For example, the method may include step S10. In this step 10, the electric heater 20 is turned on to start defrosting the exhaust gas treatment liquid. Next, in step S20, the operating current flowing through the electric heater 20 is measured. If desired, the measured operating current signal may be high frequency filtered to remove high frequency clutter signal interference in the measurement signal. Next, in step S30, it is determined whether the measured operating current signal (or the filtered current signal) is less than a predetermined current value Ip. If the judgment result is "no", go back to step S20; if the judgment result is "yes", it goes to step S30.

The predetermined current value Ip may depend on, for example, the specific configuration of the electric heater 20, such as the relationship between the shape of the heating surface and the coverage area of the liquid on the heating surface. For example, for the PTC electric heater 20 having a specific heating surface shape, the magnitude of the current flowing through the PTC electric heater is measured in advance by changing the amount of liquid covering the heating surface area of the PTC electric heater when it is operated to determine the operating current value when the liquid is insufficient to cover the heating surface of the PTC electric heater. Therefore, the current value can be used as a basis for setting the predetermined current value Ip. That is, in the technical solution of the present application, it is assumed that when the contact area of the liquid exhaust gas treatment liquid with the heating surface of the PTC electric heater in the container 100 is lower than a certain value, the resistance of the electric heater is increased and the current is decreased due to the shortage of the exhaust gas treatment liquid exchanging heat with the heating surface of the electric heater, and if the current is lower than a predetermined value, it is considered that the exhaust gas treatment liquid in the container 100 needs to be refilled.

In order to prevent frequent alarms caused by the fact that the current measurement value exceeds the standard due to unknown accidental factors, whether the measured current signal is lower than the preset current value Ip or not can be judged. If it has occurred a plurality of times, an alarm signal is generated. For example, before step S20 or at step S10, a counter T whose initial value is zero may be set. When the determination result of step S30 is yes, the counter T is incremented by 1.

In step S40, it is determined whether the counter T is greater than a predetermined value, such as an integer greater than 1, for example, 5, 10, or 100. If the judgment result is "no", it goes to step S41 where the counter T is incremented by 1. Then, the flow proceeds from step S41 to step S20. If the judgment result is "yes", it goes to step S50. At step S50, a warning signal may be issued to the driver of the vehicle to alert that a measure of filling the exhaust treatment fluid or other appropriate measure should be taken. For example, the warning signal can be presented as a beep alarm or flashing an indicator light on the dashboard or other suitable means.

The above-mentioned specific method embodiments may be implemented in an electronic control unit. For example, the present application provides a system for thawing an exhaust treatment fluid of an engine, comprising:

an exhaust gas treatment liquid container 100 for storing an exhaust gas treatment liquid;

a PTC electric heater 20 provided in the exhaust gas treating fluid container 100, the PTC electric heater 20 having a heating surface that generates heat after being activated;

a current sensor that measures the operating current of the PTC electric heater 20; and

an electronic control unit receiving a signal from the current sensor and controlling the operation of the PTC electric heater, wherein the electronic control unit is configured to instruct the current sensor to measure an operating current of the PTC electric heater after the PTC electric heater is started; and generating an early warning signal after N times of measurement results of the current sensor indicate that the measured working current value is less than a preset current value Ip every time, wherein N is an integer greater than 1.

In a preferred embodiment, the N-times measurement results are results obtained by the current sensor continuously measuring the operating current of the PTC electric heater. In another alternative embodiment, the N measurements may be accumulated by the current sensor over a period of time to measure the operating current of the PTC electric heater.

In the context of the present application, the term "liquid level" refers to the level of liquid exhaust treatment fluid in the exhaust treatment fluid container during or when the exhaust treatment fluid is thawing completely.

In a preferred embodiment, the current sensor may be a sensor integrated in the PTC electric heater. In an alternative embodiment, the current sensor may also be a sensor separate from the PTC electric heater, dedicated to measuring the current flowing through the PTC electric heater. In a preferred embodiment, the PTC electric heater is disposed at the bottom of the exhaust gas treating fluid container near the outlet.

To demonstrate the feasibility of the system and method of the present application, fig. 4 schematically shows a graph of the measured current flowing through the PTC electric heater 20 when the heating surfaces of the PTC electric heater 20 are covered with the exhaust gas treatment liquid in different areas, curve 1 representing the raw measured current value, curve 2 representing the high-frequency filtered measured current value, the ordinate representing the magnitude of the current amplitude, and the abscissa representing the time or the percentage of the area of the heating surfaces of the PTC electric heater covered by the liquid exhaust gas treatment liquid. The current through the PTC electrical heater is monitored each time it is energized, where i denotes the i-th energization of the PTC electrical heater (in fig. 4, i is an integer) and ti denotes the time at which this i-th energization is made, the percentage number between ti and ti +1 indicating the coverage of the heating surface of the PTC electrical heater 20 with liquid exhaust gas treatment liquid.

As can be seen from the graph, the coverage of the heating surface of the PTC electric heater 20 is 100% in the period from t1 to t 2. Therefore, the measured current variation does not fluctuate much. In the period from t2 to t3, since the coverage of the heating surface of the PTC electric heater 20 decreases to 80%, after the PTC electric heater is energized from time t2, since less exhaust gas treatment liquid contacts the heating surface of the PTC electric heater 20 as compared with 100% coverage, the heat generated by the heating surface is insufficiently diffused outward via heat conduction, and thus as time passes (before time t 3), the resistance of the PTC electric heater becomes large, resulting in a tendency of a decrease in the measured current. As can be seen from fig. 4, as the coverage rate decreases, the measured current value decreases more each time after the PTC electric heater 20 is energized. From time t7, the coverage of the heating surface of the PTC electric heater 20 was 30%, and the measured current value was maintained at approximately 2000mA after the PTC electric heater was energized. In three energization periods (starting at t7, t8, and t 9), the coverage rate is maintained at 30%, and the measured current value after the PTC electric heater 20 is energized is approximately 2000mA or so. Therefore, for the method shown in fig. 3, 2000mA may be set to a predetermined current value Ip. As long as the measured current value reaches or is lower than the predetermined current value Ip and is maintained for a certain time, the liquid level of the exhaust treatment fluid in the exhaust treatment fluid container 100 is considered to be lower than the normal value, and an alarm signal is generated to remind that the exhaust treatment fluid needs to be refilled.

As can be seen from fig. 4, the coverage of the heating surface of the PTC electric heater 20 by the exhaust gas treatment liquid is correlated with the current flowing through the PTC electric heater 20, and therefore, the method and system of the present application can be fully used for monitoring the liquid level when the exhaust gas treatment liquid is thawed.

By adopting the method and the system, the liquid level sensor can be saved or the liquid level sensor can be used as a supplement means, so that the liquid level condition in the waste gas treatment liquid container can be monitored more accurately. In addition, since the current of the PTC electric heater 20 can be relied upon as a reminder for filling when the exhaust treatment fluid is thawed, the volume of the exhaust treatment fluid available in the exhaust treatment fluid container is increased.

Although specific embodiments of the present application have been described herein in detail, they have been presented for purposes of illustration only and are not to be construed as limiting the scope of the application. Various substitutions, alterations, and modifications may be conceived without departing from the spirit and scope of the present application.

Claims

1. A system for defrosting an exhaust treatment fluid, in particular an aqueous urea solution, of an engine, in particular a diesel engine, comprising:

an exhaust gas treatment liquid container (100) for storing an exhaust gas treatment liquid;

a PTC electric heater (20) provided in the exhaust gas treatment liquid container (100), the PTC electric heater (20) having a heating surface that generates heat after being activated;

a current sensor that measures an operating current of the PTC electric heater (20); and

an electronic control unit receiving a signal from the current sensor and controlling the operation of the PTC electric heater, wherein the electronic control unit is configured to instruct the current sensor to measure an operating current of the PTC electric heater after the PTC electric heater is started; and generating an early warning signal after N measurements of the current sensor indicate that each measured operating current value is less than a predetermined current value (Ip), wherein N is an integer greater than 1.

2. The system of claim 1, wherein the N measurements are results of the current sensor continuously measuring the operating current of the PTC electric heater.

3. System according to claim 1 or 2, characterized in that each measurement is signal-filtered, in particular high-frequency, before being compared with a predetermined current value (Ip).

4. A system according to claim 1 or 2, wherein the current sensor is integrated within the PTC electric heater.

5. A system according to claim 1 or 2, characterized in that the predetermined current value (Ip) is determined as a function of the coverage of the heating surface of the PTC electric heater by the liquid exhaust gas treatment liquid.

6. The system of claim 1 or 2, further comprising a level sensor disposed within the exhaust treatment fluid container (100).

7. The system according to claim 5, wherein the predetermined current value (Ip) is an operating current value flowing through the PTC electric heater when a coverage of a heating surface of the PTC electric heater reaches 30%.

8. A method for monitoring a liquid level when an exhaust gas treatment fluid, in particular an aqueous urea solution, of an engine, in particular a diesel engine, is thawed, wherein the exhaust gas treatment fluid is contained in an exhaust gas treatment fluid container of an exhaust gas treatment system of a motor vehicle, in which exhaust gas treatment fluid container a PTC electric heater is arranged, the method comprising:

and generating an early warning signal after N times of measurement results indicate that the measured working current value is less than a preset current value (Ip) each time, wherein N is an integer greater than 1.

9. The method according to claim 8, wherein the N measurements are results from successive operating currents of the PTC electric heater; and/or each measurement is signal-filtered, in particular high-frequency, before being compared with a predetermined current value (Ip).

10. Method according to claim 8 or 9, characterized in that the predetermined current value (Ip) is determined depending on the coverage of the heating surface of the PTC electric heater by liquid exhaust gas treatment liquid, in particular the predetermined current value (Ip) is the operating current value flowing through the PTC electric heater when the coverage of the heating surface of the PTC electric heater reaches 30%.