DE102019212831A1 - Method for operating a pump and SCR supply system with such a pump - Google Patents

Abstract

The invention relates to a method for operating a pump with a pump chamber and an actively controllable inlet valve and an actively controllable outlet valve for the pump chamber, a pressure of a fluid to be delivered to be provided by the pump being regulated based on at least one manipulated variable, the at least one manipulated variable is selected from a control parameter (a, b, c, d, t1, t2) of the inlet valve and / or outlet valve and a pumping frequency (f) of the pump, as well as a system with such a pump.

Description

The present invention relates to a method for operating a pump, a computing unit and a computer program for carrying it out, as well as an SCR supply system with such a pump and such a computing unit.

State of the art

In the aftertreatment of exhaust gases in motor vehicles, the so-called SCR (Selective Catalytic Reduction) process can be used, in particular to reduce nitrogen oxides (NO _x). A urea-water solution (HWL) is introduced into the typically oxygen-rich exhaust gas as a reducing agent solution.

For this purpose, a metering module or metering valve can be used which comprises a nozzle in order to spray or introduce the urea-water solution into the exhaust gas flow. Upstream of an SCR catalytic converter, the urea-water solution reacts to form ammonia, which then combines with the nitrogen oxides on the SCR catalytic converter, from which water and nitrogen are produced.

The metering valve is typically connected to a delivery unit via a pressure line. A pump or feed pump of the feed unit pumps the urea-water solution from a reducing agent tank to the metering valve or to a metering module. In addition, a return is usually connected to the reducing agent tank, via which excess urea-water solution can be returned. An orifice or throttle in the return can control the return flow.

Disclosure of the invention

According to the invention, a method for operating a pump, a computing unit and a computer program for its implementation as well as an SCR supply system with such a pump and such a computing unit with the features of the independent claims are proposed. Advantageous refinements are the subject matter of the subclaims and the description below.

The invention relates to a method for operating a pump with a pump chamber with an inlet valve and an outlet valve, at least one of which is actively controllable, i.e. can be opened and closed in a targeted manner. Although the invention is described in particular with reference to an SCR supply system in which the pump is used in a delivery unit or as a delivery unit, the proposed method can also be used with other pumps as long as at least one of the inlet valve and outlet valve can be actively controlled.

An actively controllable valve (this applies to both the inlet valve and the outlet valve) is understood to mean that the opening and closing of the valve can be actively brought about in a targeted manner, for example by a magnetic switch or a valve switched by means of an electromagnet. Correspondingly, other valves - or valves conventionally used in pumps in SCR systems - are valves that open passively or automatically when a certain pressure is applied. With such conventional valves, for example, fluid can be sucked in through the inlet valve into the pump chamber in a suction phase of the pump, and then pressed out of the pump chamber in a pumping or delivery phase through the outlet valve with the inlet valve closed.

In the proposed method, a pressure to be provided by the pump of a fluid to be conveyed, that is to say for example a urea-water solution, is now regulated based on at least one manipulated variable. This at least one manipulated variable is selected from a control parameter for the inlet valve and / or outlet valve and a pumping frequency of the pump.

The control parameters of the inlet valve and / or outlet valve include in particular a control time (ie start of control or energization) of the inlet valve, an opening time of the inlet valve, a control duration (ie duration of control or energization) of the inlet valve, an opening duration of the inlet valve, a Activation time of the exhaust valve, an opening time of the exhaust valve, an activation duration of the exhaust valve and an opening duration of the exhaust valve. The activation or opening time of the inlet valve is preferably selected as a function of a dead center of a movement of a pumping element defining a minimum volume of the pump chamber, the activation or opening time of the outlet valve is accordingly selected as a function of a dead center of the pumping element defining a maximum volume of the pump chamber. In this sense, a delay time can also be used as a corresponding control parameter. It should be noted here that the actuation and opening times of a valve are usually somewhat offset in time, since, for example, a certain current first has to be built up in a magnet before an associated valve opens. In this respect, one of these two times is usually selected as the control parameter. This also applies accordingly to the end of activation and closing time or the resulting activation duration and opening duration.

In conventional piston pumps, the delivery element corresponds to the piston. For example, a so-called diaphragm pump can also be used for an SCR supply system, in which the pump chamber is closed on one side with a flexible diaphragm as a conveying element, which can be moved back and forth by means of an electromagnetic linear actuator or an electric rotary drive with an eccentric to reduce or increase the volume of the pump chamber.

The pump frequency that can be used as a manipulated variable then corresponds, for example, to a frequency with which such an electromagnetic linear actuator (in the case of a diaphragm pump or a comparable pump with a linear actuator) is moved. In the case of a conventional piston pump or diaphragm pump with a rotary drive, the pump frequency can also correspond to the speed (of a motor or electric motor with which the piston is moved - after converting the rotary into a linear movement).

By using these special manipulated variables, which is only made possible by using the actively controllable valves, different operating points of the pump can be achieved, which was previously not possible. For example, an operating point with no (or zero) volume flow of the fluid can be achieved at a certain delivery pressure (for example 9 bar between outlet and inlet) without the use of additional hardware (such as a return to the tank).

Another special feature is that the conveying direction can be reversed by means of a corresponding valve control. For this purpose, the functions of the inlet valve and outlet valve can be swapped, which is possible due to the active control. If a liquid-filled system can be damaged by freezing and the resulting ice pressure, it can be useful if the conveying direction can be reversed without additional hardware such as directional control valves in order to empty the system at the end of an operating cycle.

In general, all of the mentioned variables, i.e. the mentioned control parameters of the inlet valve and / or outlet valve and the pump frequency (simultaneously) can be used as manipulated variables, but it is expedient to actually use only some or even only one of them. The others can and should then be set to a constant value. This enables a simpler and faster adaptable control. It goes without saying that the manipulated variable or manipulated variables can also be changed during operation, if necessary or expedient.

It is particularly preferred if the at least one manipulated variable is selected from a control parameter for the inlet valve and / or outlet valve, the pumping frequency of the pump being set to a constant value. Alternatively, however, it is also preferred if the pumping frequency of the pump is used as the manipulated variable, the control parameters of the inlet valve and outlet valve each being set to a constant value.

In the case of constant speed, for example, particularly flat characteristics are possible; This means that a speed / frequency accuracy requirement on the motor or magnet (i.e. the pump drive) can be lower. In addition, a high level of control accuracy for the delivery rate within the characteristic curve is possible, since it is particularly flat. This is particularly useful only in the optimal (flat) area of the respective speed / frequency characteristic. Very high dynamics are also possible within the characteristic curve, since this is independent of the dynamics of the motor or magnet; rather, the speed or frequency is constant. It should be noted here that only a limited working range can be displayed with a fixed speed / frequency, i.e. a speed / frequency switchover may be necessary in order to cover the entire working range.

In the case of variable speed, for example, a parameter set can cover the entire working range of the pump, i.e. it is not necessary to switch the speed / frequency. It may be necessary to consider that a high speed / frequency accuracy may be necessary, i.e. a steep characteristic is required.

In order to achieve a particularly high volume flow of the fluid, it is expedient if the activation time or opening time of the inlet valve is selected such that the inlet valve opens before the dead center defining the minimum volume of the pump chamber is reached. A maximum amount of fluid can thus be introduced into the pump chamber. It goes without saying that this special selection of the control or opening time of the inlet valve can be taken into account both when using the control or opening time of the inlet valve as a manipulated variable and also with a constant value for the control or opening time of the inlet valve ( then permanently before the relevant dead center).

A computing unit according to the invention, for example a control unit of a motor vehicle such as an engine control unit or an exhaust gas aftertreatment control unit, is, in particular in terms of programming, set up to carry out a method according to the invention.

The invention also relates to an SCR supply system with a pump with a pump chamber and an actively controllable inlet valve and / or an actively controllable outlet valve for the pump chamber, as well as a computing unit according to the invention.

The implementation of a method according to the invention in the form of a computer program or computer program product with program code for performing all method steps is advantageous, since this causes particularly low costs, especially if an executing control device is used for other tasks and is therefore available anyway. Suitable data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, such as hard drives, flash memories, EEPROMs, DVDs, etc. A program can also be downloaded via computer networks (Internet, intranet, etc.).

Further advantages and embodiments of the invention emerge from the description and the accompanying drawing.

The invention is shown schematically in the drawing using exemplary embodiments and is described below with reference to the drawing.

Figure list

• 1 shows schematically an inventive SCR supply system in a preferred embodiment.
• 2 shows schematically a sequence of a method according to the invention in a preferred embodiment.
• 3rd shows schematically a sequence of a method according to the invention in a further preferred embodiment.
• 4th and 5 show characteristic curves of a mass flow of fluid in the method according to the invention in a different preferred embodiment.

Embodiment (s) of the invention

In 1 is a schematic and an example of an inventive SCR supply system 100 shown in a preferred embodiment. The SCR supply system 100 includes a conveyor unit 110 that have a pump or feed pump 200 has, which is set up, reducing agent 121 (or a reducing agent solution) as the fluid to be conveyed from a reducing agent tank 120 via a pressure line 122 to a dosing module or dosing valve 130 and which is described in more detail below. There is the reducing agent 121 then into an exhaust system 170 sprayed an internal combustion engine.

There is also a pressure sensor 140 provided (this can also be accommodated in the delivery module), which is set up to provide a pressure at least in the pressure line 122 to eat. A computing unit designed, for example, as an exhaust gas aftertreatment control device 150 is with the pressure sensor 140 connected and receives information about the pressure in the pressure line from it 122 . In addition, the exhaust aftertreatment control unit is 150 with the conveyor module 110 , and there in particular with the pump 111 and with the dosing module 130 connected in order to be able to control it.

The SCR supply system also includes 100 exemplary a return 160 , back through the reducing agent from the system (cf. Q _RL ) into the reducing agent tank 120 can be performed. In this rewind 160 is an example of an aperture or throttle 161 arranged, which offers a local flow resistance. It should be noted, however, that such a return can also be dispensed with in the proposed method with actively controlled valves.

The exhaust gas aftertreatment control device is set up to coordinate the actuators of the system based on relevant data, such as data received from the engine control device or from sensors for temperature, pressure and nitrogen oxide content in the exhaust gas, in order to transfer the urea-water solution into the exhaust tract upstream of the SCR in accordance with the operating strategy -Catalyst to be introduced. Furthermore, for example, an on-board diagnosis (OBD) monitors the components and assemblies of the exhaust gas aftertreatment system that are relevant for compliance with the exhaust gas limit values.

The pump 200 has a pump room 210 on, which is via an inlet valve 211 and an exhaust valve 212 is involved in the corresponding line. Both the inlet valve 211 as well as the exhaust valve 212 are actively controllable or controllable, ie these two valves can be opened or closed as required. In particular, the exhaust gas aftertreatment device can also be used for this purpose 150 (or possibly also another suitable computing unit, it is also conceivable that this is integrated into an electronics of the pump, there in particular the motor or valve).

In addition, the pump 200 a conveyor element 220 on to the volume of the pump room 210 to zoom in and out. At this It should be noted that the specific type of conveyor element 220 , e.g. piston or similar, is not relevant for the proposed method.

In 2 a sequence of a method according to the invention is shown schematically in a preferred embodiment. For this purpose, a curve B of a position or position of the delivery element of the pump is shown over time t, which runs between a top dead center OT and a bottom dead center UT and also represents a measure of the volume (curve between maximum and minimum volume).

In addition, control signals S _E for the inlet valve and S _A for the outlet valve are shown over time t. It can be seen that the inlet valve is activated after bottom dead center BDC, ie when the volume of the pump chamber then increases again, so that fluid can be sucked in. The outlet valve is activated accordingly after top dead center OT, ie when the volume of the pump chamber then falls again, so that fluid can be forced out.

The valves are activated to open at a specific point in time, the inlet valve at point in time t ₁ , and the outlet valve at point in time t ₂ . It can also be seen that the times t ₁ and t ₂ are spaced a period of time a and c from the previous dead center, respectively. In this sense, the _{trigger times t 1} and t _{2 can} also be defined as the delay time with respect to the corresponding dead center.

The durations of the control signals are denoted by b and d, respectively. In this way, four control parameters a, b, c and d (or instead of a and c also t ₁ and t ₂ ) of the valves can be used as manipulated variables for operating the pump.

At this point it should be mentioned that the actual opening times of the valves in practice can sometimes deviate from the corresponding times of the control signals due to necessary actuator movements, but this can be taken into account when designing a control unit.

A pump frequency of the pump can be considered as a further manipulated variable. This is indicated by the period duration of the curve B, which corresponds to the reciprocal of the pump frequency f.

In 3rd a sequence of a method according to the invention is shown schematically in a further preferred embodiment. For this, the course B is as in 2 shown over time t. In addition, a control current I _E for the inlet valve is shown. The control current IE results, for example, from a control signal, as shown in FIG 2 is shown.

Here, a curve of the control _{current I E} with control time t ₁ '(start of the current supply; opening takes place a little later, when the magnetic force is sufficiently large, here indicated with the slight bend in the current curve) is shown, which corresponds to a bottom dead center. The control parameter a according to 2 would be zero here. In comparison to this, a profile of the control current I _E is shown on the right with the control time t ₁ ″, which is before a bottom dead center. The control parameter a according to FIG 2 would be negative here. Instead of a time scale, angle information calibrated to a dead point or the previous dead point can also be used as the basis for the parameter a (or another parameter).

This shows that the use of actively controllable valves enables a particularly flexible use of control parameters as manipulated variables when the pump is in operation. The early activation of the inlet valve shown on the right can, for example, generate a particularly high volume or mass flow of the fluid.

In the 4th and 5 Characteristic curves of a mass flow M in kg / h of fluid in the method according to the invention are shown in a different preferred embodiment.

In 4th the mass flow M is plotted against the control parameter b, ie the control duration of the inlet valve, in ms as a manipulated variable. The four curves stand - from left to right - for pump frequencies f of 2,000 rpm, 1,500 rpm, 1,000 rpm and 500 rpm, which are kept constant in each case. It can be clearly seen that the mass flow M can be varied very strongly with the control parameter b alone .

At this point it should also be noted that the pump frequency f, as shown here by way of example, corresponds to a rotational speed (which is usually specified in rpm or rpm) only in the case of a pump operated in rotation. In the case of a pump with a linear actuator, however, one typically does not speak of a speed.

In 5 the mass flow M is plotted against the pump frequency f in rpm as a manipulated variable. The two curves stand - from left to right - for each of the control parameters a, b, c, d of the valves that are kept constant but are different. It can be clearly seen here that the mass flow M can also be varied very strongly with the pumping frequency alone.

Claims (12)

Method for operating a pump (200) of a delivery unit (110), in particular an SCR supply system (100), with a pump chamber (210) and an actively controllable inlet valve (211) and an actively controllable outlet valve (212) for the pump chamber (210) ), wherein a pressure to be provided by the pump (200) of a fluid (121) to be conveyed is regulated based on at least one manipulated variable, the at least one manipulated variable being selected from a control parameter (a, b, c, d, t ₁ , t ₂ ) of inlet valve and / or outlet valve and a pumping frequency (f) of the pump. Procedure according to Claim 1 , wherein the control parameters of the inlet valve and / or outlet valve include a control time (t ₁ ) of the inlet valve, an opening time of the inlet valve, a control duration (b) of the inlet valve, an opening duration of the inlet valve, a control time (t ₂ ) of the exhaust valve, an opening time of the exhaust valve , a control duration (d) of the exhaust valve, and an opening duration of the exhaust valve. Procedure according to Claim 2 , wherein the activation or opening time (t ₁ ) of the inlet valve is selected as a function of a dead center (UT) of a movement of a conveying element (220) defining a minimum volume of the pump chamber (210) and / or wherein the activation or opening time (t ₂ ) of the outlet valve is selected as a function of a dead center (OT) of the movement of the conveying element (220) which defines a maximum volume of the pump chamber (210). Procedure according to Claim 3 The activation or opening time (t ₁ ") of the inlet valve is selected, if necessary, in such a way that the inlet valve (211) opens before the dead center (UT) of the movement of the conveying element (220), which defines the minimum volume of the pump chamber, is reached. Procedure according to Claim 3 or 4th , wherein the triggering or opening time of the outlet valve is selected, if necessary, in such a way that the outlet valve (211) opens before the dead center (OT) of the movement of the delivery element (220), which defines the maximum volume of the pump chamber, is reached. Method according to one of the preceding claims, wherein the at least one manipulated variable is selected from a control parameter (a, b, c, d, t ₁ , t ₂ ) of the inlet valve and / or outlet valve, and wherein the pumping frequency (f) of the pump is set to one constant value is set. Method according to one of the Claims 1 to 5 The pumping frequency (f) of the pump is used as the manipulated variable, and the control parameters (a, b, c, d, t ₁ , t ₂ ) of the inlet valve and outlet valve are each set to a constant value. Method according to one of the preceding claims, wherein a conveying direction of the pump (200) is selected if necessary contrary to a regularly used conveying direction. Computing unit (150) which is set up to carry out all method steps of a method according to one of the preceding claims. SCR supply system (100), with a pump (200) with a pump chamber (210) and an actively controllable inlet valve (211) and an actively controllable outlet valve (212) for the pump chamber, and a computing unit (150) Claim 9 . Computer program that causes a computing unit (150) to perform all method steps of a method according to one of the Claims 1 to 8th to be carried out when it is executed on the computing unit (150). Machine-readable storage medium with a computer program stored thereon Claim 11 .

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