DE102017220842A1 - Method for controlling a holding current of a magnetic metering valve of a hydraulic system - Google Patents

Abstract

The invention relates to a method (100) for controlling a holding current of a magnetic metering valve of a hydraulic system, comprising the following steps: detecting (110) a voltage with which the solenoid metering valve is operated; Determining (120) a drive signal for a current intensity of the solenoid metering valve; and repeatedly correcting (130) the solenoid current drive signal by a correction signal based on a response of a parameter of the hydraulic system.

Description

The present invention relates to a method for controlling a holding current of a magnetic metering valve of a hydraulic system, a computer program, a machine-readable storage medium and an electronic control unit.

State of the art

Due to steadily increasing legal requirements for the emission values of internal combustion engines, the exhaust gases from internal combustion engines are subjected to an after-treatment in order to comply with the specified limit values. In order to meet these limit values, exhaust gas aftertreatment systems are used downstream of the internal combustion engine, the aim of which is to reduce the particle and nitrogen oxide concentration in the exhaust gas. The filters and catalysts used for this require that certain oxidizing / reducing agents be introduced into the exhaust line.

Typically, such agents are hydrocarbons or urea-water solutions. The hydrocarbons mentioned, e.g. Diesel fuels are used on the one hand for exothermic chemical conversion in an oxidation catalyst (DOC) with the aim of regenerating a diesel particulate filter (DPF).

The reduction of the nitrogen oxide emissions of an internal combustion engine operating with excess air, in particular a diesel internal combustion engine, can take place with the aid of the so-called Selective Catalytic Reduction Technology (SCR). In this case, a reduction of nitrogen oxides to nitrogen and water vapor is carried out, being used as a reducing agent either gaseous ammonia or ammonia in aqueous solution or urea in aqueous solution. The urea serves as ammonia carrier.

The urea is converted by hydrolysis to ammonia, which in turn reduces the actual existing SCR catalyst, which is also referred to as DENOX catalyst, the nitrogen oxides present in the exhaust gas.

The essential components of such a NOx reduction system are a reducing agent tank, a pump, a pressure regulator, a pressure sensor and a metering valve. The pump delivers the reducing agent stored in the reducing agent tank to the metering valve, by means of which the reducing agent is injected into the exhaust gas stream upstream of the hydrolysis catalyst.

In this case, the metering valve is controlled via signals of a control device, for example of the control device of the internal combustion engine, in order to supply a certain currently required amount of reducing agent. The valve is electromagnetically actuated and metered as long as the current through the solenoid coil is sufficient.

The metering valve is attached to the exhaust pipe and is exposed to a wide temperature range. However, the temperature at the metering valve must not exceed a maximum value. This must u.a. the electrical power loss in the solenoid can be kept as low as possible to prevent overheating of the coil.

To open the valve is briefly operated with a high current, the so-called pull-in current, so that the magnetic force is sufficient to overcome the spring and the pressure force. Subsequently, a small current, the so-called holding current, is sufficient to keep the valve open. If the valve closes, the control device interrupts the supply voltage, the current breaks down and the valve closes again.

Since the coil of the solenoid valve is wound from copper wire, its ohmic resistance changes with the temperature at the valve. So that the control device can set the holding current at different coil temperatures and supply voltages to the correct value, it is known in the prior art to measure the holding current and to supply it to a control circuit. For this purpose, a device for measuring the current must be present in the control device. If this is not intended, the holding current can not be regulated.

In the prior art, a second, less accurate way of controlling the current is known. For such control, one typically uses the proportionality of current and voltage across the resistor, here coil resistance, i. Ohm's Law, from. For this purpose, the voltage at the valve in the control device is measured. However, the resistance of the valve spool is unknown and must be assumed. The correct holding current will only set in controlled operation if the actual one matches the assumed coil resistance. If the actual coil resistance is lower than assumed, the holding current becomes too high, electric power loss and coil temperature rise. If the actual coil resistance is higher than assumed, a lower holding current flows. The valve could possibly close sooner, it is less metered than intended and the exhaust emissions are not met.

Disclosure of the invention

The method serves to regulate a holding current of a magnetic metering valve of a hydraulic system.

According to a preferred embodiment, the hydraulic system is arranged in an SCR catalyst system, in particular as dosing or dosing. The hydraulic system preferably comprises a tank, a pump, a pressure regulator, a pressure sensor and a metering valve. In this case, the pressure regulator is preferably realized by a control unit.

The control of the holding current of the solenoid metering occurs during the phase in which the holding current flows through the Magnetdosierventils. The control of the holding current of the solenoid metering valve should be such that the opening of the solenoid metering valve remains constant.

In a first step of the method, a voltage is detected, with which the solenoid metering valve is operated.

In a second step of the method, a drive signal for a current intensity of the solenoid metering valve is determined. This determination can e.g. by means of a calculation using a characteristic curve or a factor. Such a characteristic assigns a current value to a measured voltage value. If a factor is used, the desired drive current is obtained from the measured voltage by multiplication by the factor. Preferably, after the multiplication by the factor, an offset can be added to it.

In a third step of the method, the drive signal for the current intensity of the solenoid metering valve is repeatedly corrected by means of a correction signal based on a response of a parameter of the hydraulic system.

Here, the parameter of the hydraulic system may be a pressure of the hydraulic system or a pump speed of the pump used. (Please to inventor: can you name further parameters?)

The repeated correction of the drive signal corresponds to a regulation of the valve, in this case the solenoid metering valve. On the basis of the evaluation of at least one parameter of the hydraulic system, the valve function can be evaluated and, accordingly, the drive signal can be corrected, which in the present case occurs with the aid of a correction signal. A correction of the drive signal in turn causes a different opening behavior of the solenoid metering valve, which in turn causes a different behavior of the hydraulic system. This shows the typical characteristic of a control, which lies in the feedback of the system response to the controller.

The method has the advantage that a drive current can be found at which the metering valve must be open even without a current measurement, remains open over the entire operating temperature range and during the entire Bestromungsdauer.

According to a preferred embodiment, the repeated correction of the drive signal for the current intensity of the solenoid metering valve is carried out such that the parameter of the hydraulic system has an expected value profile. This feature has the advantage that at the desired constant opening of the solenoid metering valve and the hydraulic system shows the expected and desired value curve. In this case, the value course is understood to be a temporal value course. According to a preferred embodiment, the value course can assume a constant value.

According to a further preferred embodiment, the repeated correction of the solenoid current drive signal is terminated if a minimum current has been found at which the parameter of the hydraulic system has an expected value curve. Due to the minimum current, the magnetic metering valve advantageously heats only minimally.

According to yet another preferred embodiment, the correction signal is changed starting from a current value in both a positive and a negative direction. Preferably, this variation is repeated with decreasing distance to the value that was assumed. In this way, advantageously, a minimum value for the current can be found at which the solenoid metering valve works properly. In particular, the determination of the minimum current is so fast that the coil temperature has not changed yet. Thus, for the current coil temperature, i. for the current temperature of the solenoid metering valve, a minimum amperage can be found at which the solenoid metering valve is functioning properly.

According to a preferred embodiment, the correction signal is a product of a correction factor with the voltage and the correction factor is cyclically and gradually increased from a fixed value. Preferably, the method is terminated if a minimum current was found at which the parameter of the hydraulic system has an expected value curve. This Feature has the advantage that the calculation of the correction signal is very simple.

According to a preferred embodiment, the method for controlling the solenoid metering valve further comprises the steps described below. In step a), the correction signal is varied by a variation rate lower than a predetermined variation rate by a current value of the magnitude. Here, the variation of the correction signal takes place within a given range of values. In step b), the parameter of the hydraulic system is compared with the expected value curve. In step c), a minimum current intensity at which the parameter of the hydraulic system has an expected value profile is determined. In step d), the correction signal is set to the determined value of the minimum current. In step e), the steps a, b, c and d are repeated, wherein the last determined value of the minimum current value replaces the current value of the current strength. Here, the process does not break off, but constantly adjusts the correction signal. The predetermined variation speed is given by an average switching speed of the magnetic metering valve. (Please contact the inventor: Please check this. Please complete or correct if necessary.) This feature allows the minimum current to be advantageously adjusted to slow changes.

According to a further preferred embodiment, in case of a change in the correction signal after a waiting time, a behavior of the magnetic metering valve or a component of the hydraulic system is checked. By such a check is advantageously achieved that a possible settling of the system has subsided and has no influence on the verification measurement.

If the check shows that the solenoid metering valve or a component of the hydraulic system behaves as expected, the current correction signal will be maintained. If there is an unexpected system behavior, which can not be influenced by varying the holding current of the solenoid metering valve, then the cause for the deviating behavior lies elsewhere. In this case, the correction signal is set to a value to be determined and a corresponding message is output.

The computer program is set up to perform each step of the method, especially when running on an electronic controller or computing device. This allows the implementation of the method in a conventional control unit, without having to make any structural changes. For this purpose, the computer program is stored on a machine-readable storage medium. By loading the computer program onto a conventional electronic control unit, the electronic control unit is obtained, which is set up to regulate a holding current of a magnetic metering valve of a hydraulic system.

list of figures

• 1 zeigt eine schematische Darstellung von Komponenten eines SCR-Katalysatorsystems gemäß dem Stand der Technik.
• 2 zeigt einen schematischen Stromverlauf eines Magnetventils.
• 3 bis 6 zeigen jeweils ein Flussdiagramm eines Verfahrens zur Regelung eines Haltestroms eines Magnetdosierventils eines hydraulischen Systems gemäß einer Ausführungsform der Erfindung.

Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description.

• 1 shows a schematic representation of components of a SCR catalyst system according to the prior art.
• 2 shows a schematic current flow of a solenoid valve.
• 3 to 6 each show a flowchart of a method for controlling a holding current of a solenoid metering valve of a hydraulic system according to an embodiment of the invention.

Embodiments of the invention

1 shows in a schematic way the known components of a metering device of an SCR catalyst system. In the exhaust system 10 an internal combustion engine 11 is an SCR catalyst 12 arranged, which selectively reduces nitrogen oxides in the exhaust gas by a selective catalytic reduction (SCR). For this reaction, ammonia (NH ₃ ) is used as a reducing agent. The urea is used as a liquid urea water solution via a metering valve 13 in the exhaust system 10 upstream of the SCR catalyst 12 injected. The aqueous urea solution is placed in a reducing agent tank 14 stored. To remove the urea solution is a suction line 15 intended. The reducing agent is via a feed pump 16 from the reducing agent tank 14 conveyed and under pressure in the pressure line 17 to the metering valve 13 directed. The urea solution is tailored and precisely in the exhaust system 10 injected. In this case, the pressure of the reducing agent in the pressure line plays 17 a significant role. This reducing agent pressure is adjusted to a predefinable target pressure. For detecting the actual pressure in the pressure line 17 is a pressure sensor 18 provided, the detected pressure signals to a control unit 19 forwards. The pump 16 is used as an actuator via a signaling device of the control unit 19 controlled, so that a predetermined target pressure can be adjusted. The activation of the metering valve 13 is also required depending on a signaling of the controller 19 , The metering valve is a magnetic metering valve.

The hydraulic system of the SCR catalyst system has the following components: the tank 14 , the pump 16 , in the control unit 19 realized pressure regulator, the pressure sensor 18 and the metering valve 13 ,

2 shows a schematic current flow of a solenoid valve. Here is a current I plotted against a time t. To open the valve, the current from 0 A to a high value of the current (Please contact the inventor: Please specify a typical value and / or value range.), The so-called opening current or pull-in current I _max , Increased, so that the magnetic force is sufficient to overcome the spring and the pressure force. After reaching the opening current I _max the current drops relatively quickly to the one relatively small value of the current, the so-called holding current I _hold , (Please tell the inventor: Please specify a typical value and / or value range.) Which is sufficient to keep the valve open and which one over a relatively long period of time. (Please contact the inventor: Please give a typical value and / or value range specify.) should be kept constant. If the valve is to be closed, the control device interrupts the supply voltage, whereupon the current breaks down and the valve closes.

3 to 6 each show a flowchart of a method for controlling a holding current of a solenoid metering valve of a hydraulic system according to an embodiment of the invention.

3 shows a flowchart of a method for controlling a holding current of a solenoid metering valve of a hydraulic system according to an embodiment of the invention.

In step 110 a voltage applied to the solenoid metering valve is detected. In the next step 120 a drive signal for the current intensity of the solenoid metering valve is determined by means of a characteristic curve. In the next step 130 is corrected by means of a control the drive signal for the current of the solenoid metering valve repeatedly. This is done on the basis of a response of the pressure and the pump speed of the hydraulic system and to the extent that the pressure the pump speed of the hydraulic system has an expected value course. The correction of the drive signal is effected by adding a correction signal to the drive signal.

In the next step 131 the repeated correction of the drive signal is terminated if a minimum current has been found at which the pressure and the pump speed of the hydraulic system have an expected value course. After each change in the control signal, the measured pressure profile is compared with an expected pressure profile and a decision is made as to whether the two pressure profiles match within predefined limits. The same is done with the pump speed. Among the different drive signals in which the respective pressure curve corresponds to the expected pressure curve and the pump speed corresponds to the expected pump speed, there is a drive signal with a minimum current during the hold period to which the holding current is applied. After this minimum current has been determined, the process is terminated.

4 shows a further embodiment of the method for controlling a holding current of a solenoid metering valve of a hydraulic system.

In this embodiment of the method, the steps are 110 . 120 and 130 identical to the embodiment of the 3 ,

In following step 140 For example, the correction signal is repeatedly varied from a current value in both a positive and a negative direction with decreasing distance. This sweeps an interval by the current value, and determines, for each value of current, whether the pressure and pump speed behave as expected. As a result, a minimum current has been found at which the pressure and the pump speed have an expected value curve. Thus, in the following step 131 , which also in the embodiment of 3 occurs, the process ends.

5 shows yet another embodiment of the method for controlling a holding current of a solenoid metering valve of a hydraulic system.

In this embodiment of the method, the steps are 110 . 120 and 130 identical to the embodiment of the 3 or 4 ,

In step 150 For example, the correction factor, which multiplied by the voltage measured at the solenoid metering valve is equal to the correction signal, is cyclically and gradually increased from a fixed value. As a result, as well as in the embodiment of 4 overshadowed an interval by the current value, determining, for each value of amperage, whether the pressure and pump speed behave as expected.

Analogous to the embodiment of 4 Thus, a minimum current has been found at which the pressure and the pump speed have an expected course of values. In the following step 131 which also in the embodiments of the 3 and 4 occurs, the process ends.

6 shows a further embodiment of the method for controlling a holding current of a solenoid metering valve of a hydraulic system.

In this embodiment of the method, the steps are 110 . 120 and 130 identical to the embodiments of 3 . 4 or 5 ,

In step 161 For example, the correction signal is varied at a variation rate by a current value of the current. Here, the period corresponding to the variation speed is 10 times longer than an average period of a drive signal. (Please to inventor: Please give typical values for the period that the control signal and the period or the rate of variation in step 161 ).

In next step 162 the pressure and the pump speed of the hydraulic system are compared with the expected value curve.

In the following step 163 a minimum current is determined at which the pressure and the pump speed of the hydraulic system have an expected variation over time.

In the following step 164 the correction signal is set to the determined value of the minimum current.

Thereafter, the process returns to step 161 back and repeat the above steps 161 to 164 , where the last determined value of the minimum current value replaces the current value of the current value. As a result, the correction signal is carried continuously at the minimum current limit.

Claims (12)

Method (100) for controlling a holding current of a magnetic metering valve of a hydraulic system, comprising the following steps: Detecting (110) a voltage at which the solenoid metering valve is operated; Determining (120) a drive signal for a current intensity of the solenoid metering valve; and repeatedly correcting (130) the solenoid current drive signal by a correction signal based on a response of a parameter of the hydraulic system. Method (100) according to Claim 1 , characterized in that the parameter of the hydraulic system is a pressure or a pump speed. Method (100) according to Claim 1 or 2 , characterized in that the repeated correction (130) of the current signal of the magnetic metering valve is effected in such a way that the parameter of the hydraulic system has an expected course of values. Method (100) according to one of the preceding claims, characterized in that the repeated correction (130) of the current signal of the solenoid metering valve is terminated if a minimum current value was found at which the parameter of the hydraulic system has an expected value profile (131 ). Method (100) according to one of the preceding claims, characterized in that the correction signal is changed starting from a current value in both a positive and a negative direction (140). Method (100) according to one of the preceding claims, characterized in that the correction signal is a product of a correction factor with the voltage and the correction factor is cyclically and stepwise increased from a fixed value (150). Method (100) according to Claim 1 . 2 . 3 . 5 or 6 , further comprising: a. Varying (161) the correction signal at a variation rate that is less than a predetermined variation rate by a current value of the current magnitude; b. Comparing (162) the parameter of the hydraulic system with the expected value course; c. Determining (163) a minimum current at which the parameter of the hydraulic system has an expected value profile; d. Setting (164) the correction signal to the determined value of the minimum current, and e. Repeating steps a, b, c and d, wherein the last determined value of the minimum current value replaces the current value of the current value. Method (100) according to one of the preceding claims, characterized in that the hydraulic system is arranged in an SCR catalyst system. Method (100) according to one of the preceding claims, characterized in that the hydraulic system comprises a tank (14), a pump (16), a pressure regulator, a pressure sensor (18) and a metering valve (13). Computer program, which is arranged, each step of the method (100) according to one of Claims 1 to 9 perform. Machine-readable storage medium on which a computer program according to the preceding claim is stored. Electronic control unit, which is set up, each step of the method (100) according to one of Claims 1 to 9 perform.

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