KR102580091B1 - Method for regulating a pressure of a dosing system - Google Patents

Abstract

The invention relates to a method for controlling the pressure of a metered supply system, characterized in that the control is a two-point control and the reference input variable of the control is a function of the metered supply demand.

Description

Method for controlling pressure in metering supply system {METHOD FOR REGULATING A PRESSURE OF A DOSING SYSTEM}

The present invention relates to a method for controlling pressure in a metering supply system, a computer program, a machine-readable storage medium, and an electronic control unit.

It is known from the prior art that the drive of the pump is pressure-dependently adapted to maintain the pressure level in a metering supply system, for example an SCR system. When using a classic two-point controller, each component is activated when a limit value is exceeded. However, especially when throughput or dynamic demands are high, temporary and pronounced changes in system pressure may occur, as these controls only react to pressure variations. This effect is enhanced by the response time of the control device and the damping of the system, through which the pressure pulse changes the system pressure, which can only be measured after a delay.

In a method for controlling the pressure of a metered supply system, the control is a two-point control and the reference input variable of the control is a function of the metered supply demand.

The metering supply demand is calculated through the control unit of the metering supply system at each time and is therefore available within the control unit.

According to the above control technique, the reference input variable is the value at which the control variable is to be controlled. These values are predetermined externally. The control establishes a control deviation between the reference input variable and the control variable and correspondingly influences the system to be controlled via the control element. In a heater, for example, the temperature is the control variable, and the temperature set in the thermostat is the reference input variable. The control deviation is the difference between the set temperature and the actual temperature, and the heating power is raised or lowered correspondingly. The instantaneous value of the reference input variable is the set value. If the reference input variable does not change over time, the two concepts, reference input variable and setpoint, can be used as synonyms.

The control circuit typically functions as follows. The control variable [y(t)], also called the actual value, is a measurable variable of an existing dynamic system, also called a control path or simply a path. The control variable [y(t)] depends on the manipulated variable [u(t)] and the disturbance variable [d(t)]. The control variable [y(t)] is compared to the reference input variable [w(t)]. Control deviation [e(t)] is the difference between the actual value and the set value. In this case, the formula “e(t) = w(t) - y(t)” is applied. These control deviations are fed to a controller, from which the controller forms a manipulated variable [u(t)] corresponding to the desired temporal behavior of the control circuit. A control element can be a component of the controller, but most often it refers to a separate device.

A two-point controller is a discontinuously operating controller with two output states. Depending on whether the actual value is greater or less than the set value, either the upper output state or the lower output state is taken. Two-point controllers are typically used when the manipulated variable cannot change continuously but can only assume two states (e.g. on/off). The two-point controller reaches a steady state, but never stops. When the reference input variable changes significantly, these two-point controllers can adjust control deviations more quickly than is possible by other control methods. A known example of a two-point controller is a thermostat that controls a heating or cooling device at a constant output.

The reference input variable of the control is a function of metering supply demand. This corresponds to a prefilter. Due to this, an acceleration of the response behavior of the control device in the event of changes in metering supply demands can advantageously be achieved. Additionally, pressure drift at large flow volumes can be prevented.

According to one preferred embodiment, the intervention limit of the two-point control, i.e. the reference input variable, varies between "p _nominal - Δp/2" and "p _nominal ". In this case, "p _nominal " is the pressure to be reached on average through the control, that is to say the set pressure averaged over the course of the method, and "Δp" is the pressure rise per pump stroke. Preferably the pressure rise per stroke is a predetermined pressure difference. In order to achieve as small an absolute deviation as possible from the set pressure in normal operation, the reference input variable component, which does not depend on the metering supply demand, is set to "p _nominal - Δp/2". Accordingly, if the two-point control intervenes at a pressure of "p _nominal - Δp/2" and generates a pump stroke of "Δp", the pressure rises to "p _nominal + Δp/2". This preferably achieves that the pressure fluctuates by "p _nominal ", which is what must be achieved.

According to a further preferred embodiment, the reference input variable of said control is a linear function of the metered supply demand. In this case, the linear function preferably has a positive slope. In this case, the reference input variable is preferably raised in order to generate a pump stroke already at a higher pressure, i.e. when the deviation from the set pressure is smaller, in case the required flow increases. A further advantage is that low pressures resulting from valve activity, which follows the metering supply demand and also increases, are prevented in this way.

According to a further preferred embodiment, the reference input variable is obtained by the following function,

"은 계량 공급 요구량이며, "

"는 최대 계량 공급 요구량이다. 이러한 함수는 바람직하게는 개입 한계, 즉 참조 입력 변수가 "p_공칭 - Δp/2"와 "p_공칭" 사이에서 변화하는 특성 뿐만 아니라, 제어의 참조 입력 변수가 양의 기울기를 갖는 계량 공급 요구량의 1차 함수인 특성도 충족한다.At this time, "

" is the metered supply demand, "

" is the maximum metered supply demand. This function preferably contains the intervention limits, i.e. the characteristic at which the reference input variable of the control varies between "p _nominal - Δp/2" and "p _nominal ", as well as the positive It also satisfies the characteristic of being a linear function of metering supply demand with a slope of .

The maximum metered supply demand is preferably constant. This has the advantage that it always responds to specific demands with the same intervention threshold. However, according to a further preferred embodiment, the maximum metered supply demand may vary at each time. This has the advantage of making the system more variable.

According to a preferred embodiment, the two-point control has hysteresis. This has the advantage that controller switching from one output state to another requires a predetermined actual value change. This again prevents too frequent switching of the controller.

According to a further preferred embodiment, the metering feed system is an SCR system. Due to this, the pressure of the SCR system can advantageously be controlled.

The computer program is specifically configured to execute the respective steps of the method when executed on an electronic control unit or computational unit. This makes it possible to implement the method in a conventional control unit without the need to implement structural changes. For this purpose, the computer program is stored on a machine-readable storage medium. By installing the above computer program into a conventional electronic control unit, an electronic control unit configured to control the pressure of the metering supply system is obtained.

Embodiments of the invention are illustrated in the drawings and are described in more detail in the description below.
Figure 1 schematically shows the components of a metering supply system with a metering supply module for a reducing agent solution of an SCR catalytic converter according to the prior art.
Figure 2 is a diagram showing a controller intervention limit according to the metered supply amount for executing the pressure control method of the metered supply system according to an embodiment of the present invention.
Figure 3 is a diagram showing the operation of a metering supply pump according to an embodiment of the present invention, which depends not only on pressure but also on the set flow amount.

1 shows a part of the exhaust gas branching device 10 of an automobile internal combustion engine 13. The exhaust gas branch device 10 includes an SCR catalytic converter device 11 through which the exhaust gases of the internal combustion engine 13 flow through in the flow direction 12 . Upstream of the SCR catalytic converter device 11, a metering supply module 20 is located that injects the reducing agent solution required for the SCR catalytic converter device 11 in a required manner. The reducing agent solution stored in the tank 21 is supplied to this metering supply module 20. By the discharge pump 22, the reducing agent solution is extracted from the tank 21 through the suction line 23 and discharged under pressure through the supply line 24 to the metering supply module 20. A pressure measuring device 25 connected to the control unit 26 as well as the discharge pump 22 is connected in the supply line 24.

It is known in the prior art to use two-point control for pressure control in the supply line 24.

In this case, the reference input variable (w) is a constant set value, that is, a constant pressure value. The control deviation is the difference between the pressure in the supply line 24 measured via the pressure measuring device 25 and a constant pressure value. In this case, the control element is an actuator that changes the active state of the discharge pump 22, ie causes the stroke or non-stroke of the discharge pump 22. The control path consists of a tank 21, a discharge pump 22, a supply line 24, and a metering supply module 20. In this case, the controlled variable is the pressure in the supply line 24 measured via a pressure measuring device 25.

In this case, the two-point control functions as follows. The metering supply module 20 of the SCR system is controlled in open loop by the control unit 26 so that the required reducing agent solution is sprayed into the respective exhaust gas branch devices 10 . However, at the same time the two-point control provides a closed-loop control of the pressure measured in the supply line 24. If the pressure measured in the supply line 24 falls below a predetermined threshold, an actuator is activated, which causes a pump stroke that achieves a pressure rise by "Δp". If the pressure in the supply line 24 reaches the pressure threshold, the actuator is no longer activated and the pressure no longer rises.

)에 대한 계량 공급 요구량()의 비이다. 따라서, 이러한 비율은 0의 값과 1의 값 사이에서 변화한다. 이 경우, 최대 계량 공급 요구량은 상수이다.Figure 2 shows the controller intervention limit (w) according to the metered supply amount for pump driving, according to an embodiment of the present invention. In the case of this two-point control, the reference input variable can also be called an intervention limit, since this control intervenes at the corresponding value. In Figure 2 the controller intervention limits for pump operation, measured in units of pressure, are shown for standardized metered supply requirements. The standardized metered supply demand is the maximum metered supply demand (

Metered supply demand for ) ( ) is the ratio. Therefore, this ratio varies between the value of 0 and 1. In this case, the maximum metered supply demand is a constant.

The intervention limit is expressed by the function:

In Figure 2, the intervention limit is between 6.0 bar and 6.1 bar, approximately 6.03 bar, when there is no metered supply demand, and 6.5 bar when the metered supply demand is maximum. Therefore, “p _nominal ” is 6.5 bar, and “Δp” is approximately 0.94 bar. In this case, 4 kg/h is a typical value for the maximum metered feed demand.

Figure 3 shows the operation of a pump according to an embodiment of the present invention, which depends not only on pressure but also on the set flow rate.

In Figure 3, in the upper part of the graph, the pressure p measured in bar units in the supply line 24 is plotted against time measured in seconds. In the lower subgraph of FIG. 3, the standardized metered supply demand is plotted over the same time axis as the upper subgraph of FIG. 3.

Closed-loop control is implemented as follows. For each value of the standardized metered supply demand plotted on the time axis, the intervention limits are obtained according to FIG. 2 . If the measured pressure falls below the intervention limit at each point, two-point control intervenes and generates a pump stroke that increases the pressure in the system by a predetermined pressure value. In the upper part of the graph in Figure 3, these are each a value of 0.26 bar.

The upper part of the graph in Figure 3 lists the critical values for the pressure in the supply line, corresponding to "p _nominal ", i.e. 6.5 bar. Additionally, the corresponding pressure values are described for the points in time (t ₀ and t ₁ ) at which the two-point control is intervened. At time "t ₀ ", the lower portion of the graph in Figure 3 shows that the standardized metered supply demand is 82%. Figure 2 shows that the intervention limit corresponds to approximately 6.42 bar when slightly higher than 80% for the value of the standardized metering supply demand. This is exactly the value (p ₀ ) at which the two-point control intervenes, depicted in the upper part of the graph in Figure 3. After rising by 0.26 bar, the system pressure has a value of 6.68 bar, which is also shown in the upper graph of Figure 3.

In further progress after "t ₀ " the system pressure is lowered in a number of steps until the two-point control intervenes again. This happens two more times between time "t ₀ " and time "t ₁ ". At time "t ₁ ", the standardized metered supply demand has a value of 70%. From Figure 2, an intervention limit of approximately 6.35 bar is obtained for this value, which is the value as "p ₁ " for which the two-point control intervenes, shown in the upper part of the graph in Figure 3. After an increase of 0.26 bar, the system pressure has a value of 6.61 bar, which is also shown in the upper part of the graph in Figure 3.

Claims (9)

In a method for controlling the pressure of a metering supply system,
The control is a two-point control, and the reference input variable of the control is a function of metering supply demand,
The intervention limit of the two-point control varies between "p _nominal - Δp/2" and "p _nominal ", where "p _nominal " is the pressure to be achieved on average through the control, and "Δp" is the pressure per pump stroke. A method of controlling pressure in a metering supply system, characterized in that the rise. delete The method of claim 1, wherein the reference input variable for the control is a linear function of the metered supply demand. The method of claim 1 or 3, wherein the reference input variable is obtained by the following function,

At this time, " " is the metered supply demand, " " is a pressure control method of a metering supply system, characterized in that "is the maximum metering supply demand. 4. A method according to claim 1 or 3, wherein the two-point control has hysteresis. The method of claim 1 or 3, wherein the metering supply system is an SCR system. A computer program stored on a machine-readable storage medium and configured to execute each step of the method according to claim 1 or 3. A machine-readable storage medium storing the computer program according to claim 7. An electronic control unit, configured to execute each step of the method according to claim 1 or 3.

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