DE102021204407A1 - Method of operating a pump and fluid supply system - Google Patents

Abstract

The invention relates to a method for operating a pump (210) with a pump chamber (220), an element (225) delimiting the pump chamber (220) and an electric motor (240) which is connected to the element delimiting the pump chamber (220) via an eccentric drive (225) for varying a volume of the pump chamber (220), the electric motor (240) being controlled in such a way that during a delivery phase (PF) the pump is specified at least on average a higher speed (n) than during a suction phase ( Ps) of the pump.

Description

The present invention relates to a method for operating a pump, a computing unit and a computer program for executing it, and a fluid supply system.

Background of the Invention

The so-called SCR method (Selective Catalytic Reduction) can be used in the after-treatment of exhaust gases in motor vehicles, in particular for the reduction of nitrogen oxides (NO _x ). A urea-water solution (HWL) is introduced as a reducing agent solution into the typically oxygen-rich exhaust gas.

A dosing module or dosing valve can be used for this purpose, 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, resulting in water and nitrogen.

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

Disclosure of Invention

According to the invention, a method for operating a pump, a computing unit and a computer program for executing it, and a fluid supply system with the features of the independent patent claims are proposed. Advantageous configurations are the subject of the dependent claims and the following description.

The invention relates to a method for operating a pump, which has a pump chamber, an element delimiting the pump chamber and an electric motor which (or its rotor shaft) is coupled via an eccentric drive to the element delimiting the pump chamber in order to vary a volume of the pump chamber. having. In other words, the element delimiting the pump chamber is connected or coupled eccentrically to the shaft or the rotor. This element is preferably a membrane which is coupled to the eccentric via a connecting rod, for example. This is then a so-called membrane pump, as is typically used for the already mentioned SCR supply systems—or also other fluid supply systems.

In addition, the pump chamber can be delimited by at least one, preferably two, valves which connect the pump chamber to an inlet or an outlet. At least one of these valves, but in particular both, are expediently actively controllable. The two valves serve in particular as an inlet valve and an outlet valve. In particular, in a suction phase of the pump, fluid should be sucked into the pump chamber through the inlet valve and then in a pumping or delivery phase through the outlet valve—with the inlet valve closed—pushed out of the pump chamber.

An actively controllable valve (this applies to both an inlet valve and the outlet valve) is to be understood here as meaning that the opening and closing of the valve can be actively brought about in a targeted manner, for example by an electromagnetic actuator with a coil and an armature, so that the valve can be switched by suitably energizing the coil.

A particular advantage of pumps with actively controllable valves is that the pumps can be operated in more or less any way thanks to the individual control of the valves, e.g. with a pumping direction opposite to the regular pumping direction. In an SCR supply system, in which a fluid such as a urea-water solution is pumped from a fluid tank to a dosing module, this can mean, for example, that the fluid can also be pumped back from the dosing module back into the fluid tank if required can. For this purpose, the valves would only have to be opened and closed in a corresponding manner. Alternatively, however, valves can also be used which open passively or automatically when a certain pressure is applied, for example check valves.

As has been shown, the eccentric drive for the membrane (or possibly another element delimiting the pump chamber) leads to a highly transient, required drive torque. During the delivery stroke, this moment has an approximately sinusoidal curve. Deviations from the sinusoidal shape are caused, for example, by the membrane stiffness and the pressure profile in the pump chamber.

During the suction phase, however, the torque required is significantly reduced. This different drive or torque requirement makes it necessary to control the electric motor very dynamically. Since a measurement of the torque is typically not possible or at least not provided for, the torque of the electric motor can be controlled using the speed. The rotational speed can typically only be recorded at specific angles or angle values of the shaft, for example every 10°. The current speed can therefore only be determined afterwards (e.g. every 10°). In addition, limitations in the electrical hardware often lead to delayed control of the motor torque.

This leads to strong braking of the electric motor at the beginning of the delivery phase or the delivery stroke of the pump and to acceleration of the electric motor at the end of the delivery phase. The average speed is lower during the pumping phase and higher during the suction phase. The delivery phase is also longer, which leads to an increased power requirement of the electric motor and heats it up through the ohmic resistances. At a very low engine speed, the electric motor can even overheat, which leads to the electric motor being switched off.

The sucking phase, on the other hand, is shortened; at this stage the pump room must be filled. Since typically only the ambient pressure is available for filling the pump chamber, the filling speed is limited by the pressure difference between the tank pressure and the vapor pressure of the reducing agent, as well as hydraulic resistance; the filling time should therefore be as long as possible. The hydraulic resistances are determined by the holes in the inlet valve and the existing filters (typically to protect the components) and are usually already minimized within the scope of the technical possibilities. For complete filling, especially at high speeds and delivery rates, the suction phase should be as long as possible so that high delivery rates are possible even under unfavorable boundary conditions such as high filter loading, high ambient temperature and low ambient pressure.

Against this background, it is proposed that the electric motor is controlled in such a way that during the delivery phase of the pump, a higher speed is specified, at least on average, than during the suction phase of the pump. In addition, it can also be provided to regulate the speed of the electric motor to the respective desired value; different target values for the speed are specified for the delivery phase and for the suction phase. The target value for the delivery phase (or at least part of it) is correspondingly higher than the target value for the suction phase (or at least part of it), in particular the target value for the delivery phase (or at least part of it) is higher than a specified reference value that for the sucking phase (or at least a part of it), however, is lower than the reference value. Based on a full revolution of the shaft of the electric motor, the reference value should then be reached on average. This specified reference value can be a setpoint value that has been used up to now, which indicates, for example, a desired mean speed. This is used, for example, to specify a desired delivery rate for the pump.

In this way, the disadvantages of the previous engine control are eliminated; at the beginning of the delivery phase, the electric motor is accelerated and at the end of the delivery phase and thus at the beginning of the suction phase, it is decelerated. In comparison to the specification of a constant target value, the delivery phase is therefore shortened and the suction phase lengthened. However, the average speed or speed (the reference value mentioned) can remain constant.

Due to the increased engine speed during the delivery phase, the average torque of the electric motor can be significantly reduced; this also significantly reduces the power loss of the electric motor. The power requirement is also reduced, the average current is lower. In addition, the peak current can be reduced, which means that the electric motor no longer heats up as much. The risk of the electric motor stopping is reduced. This is particularly advantageous and important at low speeds. At high speeds, a better filling of the pump chamber is achieved and a higher delivery rate can be achieved, especially in negative or poor environmental conditions.

The deviations of the target values for the rotational speed from the reference value (or a previously used target value) are preferably chosen in such a way that the result is a run that is as stable as possible. In this regard, reference is also made to the explanations for the figures. The average actual speed in the delivery phase should be as high as possible and as low as possible in the suction phase. Since the electric motor is limited in its maximum torque and in its dynamics, the change in the desired setpoint speed preferably does not take place directly at a dead center (top dead center or bottom dead center) of the eccentric or the membrane, but somewhat earlier. In this regard, reference is also made to the explanations for the figures.

A computing unit according to the invention, e.g. a control unit of a motor vehicle, an exhaust gas aftertreatment control unit or a pump control unit, is set up, in particular in terms of programming, to carry out a method 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 carrying out all method steps is advantageous because this causes particularly low costs, especially if an executing control unit is also 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. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and refinements of the invention result from the description and the attached drawing.

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

character list

• 1 shows schematically a fluid supply system with a pump in which a method according to the invention can be carried out.
• 2 shows schematically a pump in which a method according to the invention can be carried out.
• 3 shows curves of speed, torque and stroke in a method not according to the invention.
• 4 and 5 show curves of speeds, torque and stroke in a method according to the invention in a preferred embodiment.
• 6 shows curves of speed, torque and stroke in a method not according to the invention.
• 7 and 8th show curves of speeds, torque and stroke in a method according to the invention in a preferred embodiment.

embodiment(s) of the invention

In 1 a fluid supply system 100 embodied as an SCR supply system is shown schematically and by way of example, in which (or in the case of a pump present there) a method according to the invention can be carried out. The SCR supply system 100 includes a pump or delivery pump 210 with a pump chamber 220, two actively controllable valves 221 and 222 for the pump chamber 220 and a filter 230. These components together form an example of a delivery unit 200, which is available as a structural unit, for example can be asked.

In the case of a regular conveying direction, valve 221 serves as an inlet valve, while valve 222 serves as an outlet valve. In addition, the pump 210 has a delivery element 225 in order to increase and decrease the volume of the pump chamber 220 . The conveying element 225 can be a membrane, for example, as will be explained in more detail below.

The pump 210 is now set up to deliver reducing agent 121 (or a reducing agent solution) as the fluid to be delivered from a fluid tank 120 via a pressure line 122 to a dosing module or dosing valve 130 . There, the reducing agent 121 is then sprayed into an exhaust line 170 of an internal combustion engine.

Furthermore, a pressure sensor 140 is provided (this can also be accommodated in the delivery unit 200 ), which is set up to measure a pressure at least in the pressure line 122 . A computing unit 150, embodied, for example, as an exhaust gas aftertreatment control device, is connected to pressure sensor 140 and receives information from it about the pressure in pressure line 122. Exhaust gas aftertreatment control device 150 is also connected to delivery unit 200, there in particular to pump 210, and to dosing module 130. to be able to control them. This also includes activation of the actively controllable valves 221 and 222.

In addition, the SCR supply system 100 includes, for example, a return 160 through which the reducing agent can be returned from the system to the fluid tank 120 . In this return 160, for example, an orifice or throttle 161 is arranged, which offers a local flow resistance. However, it should be noted that such a return can also be omitted in a pump with actively controlled valves.

The exhaust gas aftertreatment control unit is set up to use relevant data, such as data received from the engine control unit or from sensors for temperature, pressure and nitrogen oxide content in the exhaust gas, to coordinate the system's actuators in order to inject the urea-water solution into the exhaust system in front of the exhaust tract in accordance with the operating strategy Introduce SCR catalytic converter. 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.

In 2 is a schematic of a pump 210 in which a method according to the invention can be carried out, in more detail than in FIG 1 shown in a sectional view. In addition to the pump chamber 220 and two actively controllable valves 221 and 222 for the pump chamber 220, the pump 210 has, in particular, an element 225 designed as a membrane, which delimits the pump chamber 220.

In addition, an electric motor 240 is provided, on whose runner (or rotor) 245 with a rotor shaft 246 by means of an eccentric 247 (cf. angle φ) a connecting rod 250 is attached, which is also connected to the membrane. In this way, an up and down movement of the membrane 225 can be achieved by a rotational movement of the runner 250 . It should be noted here that an eccentric can also be formed, for example, by the connecting rod being fastened eccentrically to the rotor 245, i.e. at a distance from the shaft 246. Overall, the electric motor 240 or its rotor shaft 246 is accordingly coupled via an eccentric drive 246, 247 to the membrane 225 delimiting the pump chamber 220 in order to vary a volume of the pump chamber 220.

The two valves 221 and 222 here have electromagnetic actuators, each with a coil 223 and an armature 224, by means of which a suitable element can be actuated to release a flow, i.e. to open the valve, or to block it, i.e. to close the valve shut down.

In 3 courses of speed, torque and stroke are shown in a non-inventive method for operating a pump, as explained above. For this purpose, the torque M of the electric motor and the speed n (upper diagram) as well as a stroke h of the diaphragm (lower diagram) are plotted against time t. P _S denotes a suction phase, P _F denotes a delivery phase.

In this example, a setpoint value of e.g. 500 rpm is constantly specified for the speed. The mean moment here is approx. 67 Nmm.

In 4 are curves of speeds and stroke in a method according to the invention in a preferred embodiment for operating a pump, as explained above, shown. A reference value for the rotational speed _is shown with n set _, with an actual value for the rotational speed with n and with n _ref a reference value for the rotational speed.

The target value for the rotational speed is higher for the delivery phase, for example 650 rpm, and lower for the suction phase, for example 400 rpm, than the reference value of 500 rpm, for example. The reference value should be reached on average. The possible increases and decreases in speed depend, for example, on the engine power, the torque from the eccentric, the inertia of the drive, the speed detection and the controller. At high speeds, there is also an increase in pressure in the pump chamber at the beginning of the delivery stroke. This is caused by the inertia of the fluid and the potential opening speed of the discharge valve. This maximum pressure must not exceed the opening pressure set by the spring tension of the spring on the tank-side valve.

The spring preload force is in turn limited by the possible magnetic force and the bearable load of the seat. Due to the large number of parameters to be taken into account, the best possible value for the speed increase can be determined, e.g. with the help of a simulation or a test.

A possible procedure for an application is as follows: A speed reduction during the intake stroke is specified as a function of the nominal speed, the speed increase is controlled in such a way that the nominal speed is reached. If the nominal speed is no longer reached, the speed reduction is reduced. If the pressure peak in the pump chamber becomes too great, the speed reduction is also reduced. The reverse procedure is also possible, first specifying the speed increase and then controlling the reduction so that the desired nominal speed is reached.

The average speed can be calculated in a simplified manner without acceleration times. The speed is the inverse of the time per revolution. The total time per revolution consists of the time for the suction stroke and the time for the delivery stroke. By converting it into angles, it follows that when lowering equals elevation and the same angle, the average speed is lower than the desired average speed. So the lift must be larger, or the angle for the high speed larger.

In 5 the associated courses of speed n and moment M (upper diagram) as well as stroke h (lower diagram) are shown enlarged for the first two periods. P _S denotes a suction phase, P _F denotes a delivery phase.

It can be seen that when a bottom dead center UT of the membrane is reached (correspondingly applies to eccentrics), ie at minimum stroke h, a transition from the suction phase to the delivery phase takes place. Accordingly, there is a transition from the delivery phase to the suction phase at top dead center OT. It can be seen that the suction phase s last longer than the funding phases, so that the deviation of the target value from the reference value is smaller. In comparison with 4 it becomes clear that the respective target values are already changed before the respective dead center UT or OT is reached.

If the speed should not or cannot be lowered via a negative motor torque, then it must be lowered via the load. The load is only present up to TDC. The speed must therefore be reduced via the load before TDC. As the consideration above shows, the speed increase should not be too short, otherwise the speed increase will be too high. With limited engine torque, the speed can only be increased with a small load. Therefore, the speed before BDC is increased.

It is also advantageous not to change the speed too much while the valve is being switched on and off, because this reduces the accuracy of the opening and closing times at the correct angular position in the event of speed fluctuations.

This design makes the engine run more stable and significantly reduces the energy requirement. The average moment can be lowered to about 30 Nm, for example.

the 6 , 7 and 8th show an example comparable to that 3 until 5 , but with a mean speed of 1,000 rpm instead of 500 rpm (in 6 is it according to the setpoint, in 7 the reference value). For the other explanations of the figures, refer to the above explanations 3 until 5 referenced, which apply here accordingly. As a result, it can be seen that the average torque of the membrane has been reduced from approx. 60 Nmm to approx. 26 Nmm.

Overall, therefore, a very energy-efficient operation of the pump is possible with the proposed method.

Claims (11)

Method for operating a pump (210) with a pump chamber (220), an element (225) delimiting the pump chamber (220) and an electric motor (240) which, via an eccentric drive, is connected to the element (225) delimiting the pump chamber (220) for Variation of a volume of the pump chamber (220) is coupled, the electric motor (240) being controlled in such a way that during a delivery phase (P _F ) the pump is specified at least on average higher speed (n) than during a suction phase (P _S ) the pump. procedure after claim 1 , wherein the speed (n) of the electric motor (240) _is set or regulated in at least part of the delivery phase (P _F ) to a higher desired value (n set ) than for at least part of the suction phase (P _S ). procedure after claim 2 , wherein the electric motor (240) is controlled in such a way that the speed (n), based on a full revolution of a rotor shaft (246) of the electric motor (240), reaches a predetermined reference value (n _Ref ) on average. procedure after claim 2 or 3 _, the target values (n target ) of the speed already being specified before a dead center (OT, UT) of the eccentric drive (247) is reached for the subsequent phase (P _F , P _S ). Method according to one of the preceding claims, wherein the element (225) delimiting the pump chamber (220) is designed as a membrane. Method according to one of the preceding claims, wherein the pump chamber is delimited by means of at least one valve (221, 222) which has an electromagnetic actuator with a coil (223) and an armature (224) and can therefore be actively controlled. Method according to one of the preceding claims, in which a fluid (121) is conveyed in a fluid supply system, in particular an SCR supply system (100), by means of the pump. Arithmetic unit (150) which is set up to carry out all method steps of a method according to one of the preceding claims. Fluid supply system, in particular SCR supply system (100), with a pump with a pump chamber (220), two valves (221, 222) closing off the pump chamber, and with an electric motor (240) with which a pump chamber (220) delimiting Element (225), which is eccentrically coupled to the electric motor (240), is movable back and forth, and with a computing unit claim 8 . Computer program that causes a computing unit (150) to carry out all the method steps of a method according to one of Claims 1 until 7 to be performed when it is executed on the computing unit. Machine-readable storage medium with a computer program stored on it claim 10 .

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