Method and device for temperature measurement in a dosing valve

Abstract

The invention relates to a method for determining a coil temperature (T coil ) a magnetic coil (56) of an electromagnetically operated metering valve, in particular in a reducing agent injection system (1), with the following steps: - Providing a metering valve so that it can be operated by time-controlled application of an operating voltage to the solenoid coil (56) to open the metering valve; - Control (S3) with several voltage pulses of the operating voltage so that the dosing valve does not open; - Determining (S4) a current response of the current through the magnetic coil; - Determine (S5) a resistance value (R coil ) depending on the current response; - Determine (S6) the coil temperature (T coil ) of the magnetic coil (56) depending on the resistance specification.

Description

Technical area

[0001] The invention relates to metering valves, in particular for reducing agent injection systems, and further to methods for temperature monitoring of coils of a metering valve, in particular in a reducing agent injection system. Technical background

[0002] To reduce nitrogen oxides in the combustion exhaust of an internal combustion engine, a reducing agent, typically an aqueous urea solution, is fed into the exhaust system. The reducing agent is supplied under pressure in a pressure line using a supply module and injected into the exhaust system via a metering unit with one or more metering valves. The amount of injected reducing agent is determined by adjusting the opening time of a metering valve in the metering unit.

[0003] Due to their proximity to the combustion exhaust gas, metering valves in reducing agent injection systems are exposed to high temperatures. To ensure the reliable function of the metering valves, temperature monitoring is necessary, as excessive temperatures can cause damage or malfunction of the metering valves.

[0004] The ohmic resistance of the solenoid coil depends on the temperature, so the temperature of the solenoid coil can be determined from the resistance value. Previous methods for measuring the temperature of the solenoid coil in the metering valve therefore involve brief activation to induce a saturation current in the solenoid coil and thus perform a resistance or inductance measurement. However, by briefly controlling the metering valve with the saturation current, the valve is briefly opened and reducing agent is supplied to the exhaust tract. If this measurement is performed outside of the regular metering process, an excess amount of reducing agent is injected into the exhaust tract.

[0005] The reducing agent is typically an aqueous urea solution, which decomposes into water and ammonia in the exhaust tract. Since ammonia emissions are subject to strict limits, this type of temperature measurement method is undesirable, as it could lead to ammonia emissions.

[0006] The document DE 10 2021 204 406 A1 discloses a method for controlling a solenoid valve which is controlled to open a flow opening in a first control section and a subsequent second control section, in each of which a voltage is applied to a solenoid coil of the solenoid valve in order to move a magnet armature to open the flow opening, wherein the voltage is clocked in the first control section and applied to the solenoid coil in the second control section as a DC voltage, wherein a time duration of the first control section is selected to be at least long enough for the solenoid valve to open.

[0007] The document DE 10 2011 088 708 A1 discloses a method for determining the temperature of a solenoid coil of a reciprocating piston pump, comprising determining a supply voltage of a lifting magnet of the reciprocating piston pump, determining a coil current of the solenoid coil, calculating the electrical resistance of the solenoid coil, and determining a temperature increase of the solenoid coil compared to a reference temperature from the electrical resistance of the solenoid coil and an electrical resistance of the solenoid coil at the reference temperature.

[0008] It is therefore an object of the present invention to provide an improved method for temperature measurement in a metering valve in a metering unit, in particular of a reducing agent injection system, in which the metering valve does not open during the temperature measurement and thus no undesired additional injection takes place, in particular in a reducing agent injection system. Disclosure of the invention

[0009] This object is achieved by the method for operating a metering unit, in particular a reducing agent injection system, with a metering valve according to claim 1 and a corresponding device and a reducing agent injection system according to the independent claims.

[0010] Further embodiments are specified in the dependent claims.

[0011] According to a first aspect, a method for determining a coil temperature of a solenoid coil of an electromagnetically operated metering valve, in particular in a reducing agent injection system, is provided, comprising the following steps: - Providing a metering valve so that it can be operated by time-controlled application of an operating voltage to the solenoid coil to open the metering valve; - Control with several voltage pulses of the operating voltage so that the dosing valve does not open; - Determining a current response of the current through the solenoid coil; - Determining a resistance value depending on the current response; - Determine the coil temperature of the solenoid coil depending on the resistance value.

[0012] The requirements for reducing pollutant emissions from vehicles with internal combustion engines are becoming increasingly stringent. Exhaust gas purification by injecting an aqueous urea solution as a reducing agent makes an important contribution to reducing nitrogen oxides in combustion exhaust gases. However, free ammonia can be produced during the conversion of the urea solution, so that an unbalanced supply of urea solution to the exhaust system can result in ammonia being released into the environment. Due to strict guidelines regarding the concentration of emitted ammonia, the supply of urea solution to the exhaust system must be closely monitored.

[0013] For the operation of a dosing unit in a reducing agent injection system, precise knowledge of the coil temperature of a solenoid coil of a dosing valve used for the targeted supply of reducing agent into the exhaust tract is necessary. For cost reasons, such temperature measurement is usually performed without a temperature sensor, but rather by measuring temperature-dependent electrical parameters of the dosing valve coil.

[0014] The metering valve coil can only be controlled by applying a predetermined operating voltage. The current method therefore involves briefly controlling the metering valve and measuring the current to obtain an indication of the metering valve's ohmic resistance. The resistance reading can then be assigned to a specific coil temperature. This method results in the metering valve opening when current is applied for temperature measurement, and reducing agent is injected into the exhaust tract. However, this is not permitted because ammonia emissions must be avoided.

[0015] The metering of reducing agent is determined by the opening duration of the metering valve, which is set by a control pulse (square-wave pulse) of a predetermined duration. To prevent the metering valve from opening, the above method provides for energizing the solenoid coil of the metering valve of the metering unit only in such a way that no movement of the metering valve occurs. This means that the control pattern of the voltage pulses for controlling the metering valve is selected such that the restoring force of a return spring of the metering valve cannot be overcome, thus preventing the valve pin of the metering valve from opening.

[0016] It can be provided that the plurality of voltage pulses of the operating voltage correspond to a pulse-width-modulated measuring voltage, the duty cycle of which is selected such that no movement or opening of the dosing valve occurs, or to a control pattern of several voltage pulses in which no movement or opening of the dosing valve occurs.

[0017] Such control can be achieved using a pulse-width modulated control system with a low duty cycle. The duty cycle of the pulse-width modulated control of the metering valve can be selected such that the restoring force acting on the valve pin of the metering valve cannot be overcome by the actuating force of the solenoid controlled by the PWM measurement signal. This ensures that the metering valve remains closed during the resistance measurement, and no reducing agent is injected.

[0018] When the metering valve is controlled with a pulse-width modulated control pattern, an effective voltage is established, at which a current response can be measured. This current corresponds to an effective coil current, which represents a resistance value or allows the determination of an ohmic resistance value for the metering valve coil.

[0019] In particular, the current response may correspond to an effective coil current after a predetermined period of time which corresponds at least to the period of a transient response. can be determined depending on the resistance value. Due to the temperature dependence of the conductor of the solenoid coil, this resistance value can be determined based on the temperature of the solenoid coil, in particular using a predefined assignment function or assignment table.

[0020] Temperature monitoring can be implemented depending on the coil temperature. For example, the operation of the dosing valve can be stopped or throttled if a specified temperature threshold is exceeded.

[0021] According to a further aspect, an apparatus for carrying out the above method is provided.

[0022] According to a further aspect, a reducing agent injection system for injecting reducing agent into an exhaust tract of an internal combustion engine is provided, comprising: - a metering valve with a solenoid coil for moving a valve pin against a restoring force; - the above device. Brief description of the drawings

[0023] Embodiments are explained in more detail below with reference to the attached drawings. They show: Fig. 1 a schematic representation of a reducing agent injection system for injecting reducing agent into an exhaust tract of a motor vehicle, Fig. 2 a schematic cross-sectional view through a metering valve for the reducing agent injection system according to Fig. 1; Fig. 3 a circuit diagram of a driver circuit for controlling the magnetic coil; and Fig. 4 is a flow chart illustrating a method for determining the temperature of a coil of a metering valve of a metering unit of the reducing agent injection system for performing temperature monitoring; and Fig. 5 the time course of a coil current I after applying the control pattern. Description of embodiments

[0024] Fig. 1 shows a reducing agent injection system 1 with a reducing agent tank 2, from which reducing agent is pumped into a pressure line 4 via a supply module 3. The supply module 3 has a reducing agent pump 31, which can supply reducing agent under pressure in the pressure line 4. A pressure sensor 32 is provided in the supply module 3 to regulate the pressure level in the pressure line 4. Furthermore, the supply module 3 can have a pressure damper 33 to dampen pressure fluctuations.

[0025] The pressure line 4 is connected to a dosing unit 5 through which reducing agent is injected into an exhaust tract 6 of an internal combustion engine or an exhaust aftertreatment device.

[0026] The injection is controlled or regulated using a control unit 10 in a manner known per se for nitrogen oxide reduction.

[0027] Fig. Figure 2 shows a cross-sectional view of the structure of an electromagnetically operated metering valve for the metering unit 5 of the reducing agent injection system 1. The metering valve has a housing 51 and is essentially circular-cylindrical in shape. Arranged inside is a pressure chamber 52 as a hollow space, which has an outlet opening 53 in the region of the metering valve head. A valve pin 54 is axially displaceably mounted within the housing 51 or the pressure chamber 52, and is pressed against the outlet opening 53 by a spring element 55, thereby closing it.

[0028] A solenoid coil 56 is also arranged in the pressure chamber 52. The solenoid coil 56 works together with a valve pin armature (not shown here) to displace the valve pin 54 against the spring force of the spring element 55, thereby opening the outlet opening 53. In the closed state, the valve pin 54 rests sealingly on the outlet opening 53.

[0029] Through an inlet opening 57 in a region of the housing 51 opposite the outlet opening 53, a reducing agent, such as a urea-water solution (AdBlue), flows from the pressure line 4 into the pressure chamber 52. If the valve pin 54 is displaced by the solenoid coil 56, the outlet opening 53 is opened, and the reducing agent is fed through the outlet opening 53 into an exhaust tract of an internal combustion engine.

[0030] Fig. Figure 3 schematically shows a control stage 6 for the solenoid coil 56 of the metering valve. The control stage 6 comprises a high-side semiconductor switch 61 (e.g., MOSFET) and a low-side semiconductor switch 62 (e.g., MOSFET), between which the solenoid coil 56 of the metering valve is arranged. A freewheeling diode 64 is arranged between the low-side semiconductor switch 62 and the high supply potential VDD to divert voltage spikes due to an induced voltage when the high-side semiconductor switch 61 and the low-side semiconductor switch 62 are turned off.

[0031] The control is achieved by separately controlling the high-side semiconductor switch 61 and the low-side semiconductor switch 62 with the control unit 10, whereby the high-side semiconductor switch 61 remains closed to apply a pulse-width-modulated signal, while the pulse-width-modulated measurement signal is realized by switching the low-side semiconductor switch 62. The ohmic resistances of the magnetic coil 56 and the supply lines are connected to the parasitic resistor 65 (R wire ) is taken into account in the circuit diagram.

[0032] Fig. 4 illustrates the method for monitoring a temperature of the coil 56 of the metering valve for the metering unit 5 of the reducing agent injection system 1.

[0033] The method can be implemented in the control unit 10.

[0034] In step S1, the dosing unit is controlled regularly or cyclically to carry out exhaust gas aftertreatment, in particular to inject reducing agent into the exhaust tract in order to convert nitrogen oxides present there.

[0035] In step S2, the enable conditions are checked to determine whether a measurement of the dosing valve coil temperature may be performed. If the enable conditions are met (alternative: Yes), the process continues with step S3; otherwise (alternative: No), the process returns to step S1.

[0036] In step S3, a pulse-width-modulated control of the dosing valve coil is performed for a predetermined period of time. The pulse-width-modulated control is performed with a duty cycle r dc , which has an effective current I coil in the magnetic coil 56. The predetermined time period is selected so that the coil current I coilis at a steady level.

[0037] Fig. Figure 5 shows the time course of the coil current I after applying the control pattern with a cyclic energization of the solenoid coil 56. It can be seen that the average effective coil current I coil increases in a sawtooth pattern until it reaches a steady-state value and varies around a constant mean value. A measurement of this steady-state value of the coil current I coil then takes place in a given measuring window F.

[0038] In step S4, the effective current I coil measured by the magnetic coil 56.

[0039] The on-voltage of the pulse-width modulated measuring voltage corresponds to U batt The voltage required for pulse width modulation corresponds to U coilThe duty cycle is selected to produce a dosing valve actuating force that is lower than the return force for valve pin 54. A current measurement is performed, which indicates an effective coil current. The temperature-dependent coil resistance R coil is then calculated according to the following formulas: Rcoil=UcoilIcoil=(UBatt−UDrop)×rdc−UFreewheeling×(1−rdc)Icoil UDrop=Rdrop×Icoil UFreewheeling=UDiode+RFreewheeling×Icoil Rdrop=Rwire+RHS_PS+RLS_Ps RFreewheeling=RHS_PS+Rwire where R HS_PS and R LS_PS correspond to the on-resistances of the high-side semiconductor switch 61 and the low-side semiconductor switch 62.

[0040] Then, using the above formulas, in step S5 the coil resistance is calculated according to the formula Rcoil=(UBatt−(Rwire+RHS_PS+RLS_PS)×Icoil)×rdc−(UDiode+(RHS_PS+Rwire)×Icoil)×(1−rdc)Icoil determined.

[0041] In step S6, the coil resistance is converted into a coil temperature T coil converted. Tcoil=RcoilR20−1α+20°C

[0042] Where α corresponds to a temperature coefficient for copper, and R20 is the resistance of the coil at a temperature of 20°C.

[0043] In step S7, temperature monitoring can be carried out based on the coil temperature T thus determined. coil In particular, if a threshold temperature is exceeded, the control power may be throttled or the injection system may be shut down. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2021 204 406 A1

[0006] DE 10 2011 088 708 A1

[0007]

Claims

[1] Method for determining a coil temperature (T coil ) a magnetic coil (56) of an electromagnetically operated metering valve, in particular in a reducing agent injection system (1), with the following steps: - Providing a metering valve so that it can be operated by time-controlled application of an operating voltage to the solenoid coil (56) to open the metering valve; - Control (S3) with several voltage pulses of the operating voltage so that the dosing valve does not open; - Determining (S4) a current response of the current through the magnetic coil; - Determine (S5) a resistance value (R coil ) depending on the current response; - Determine (S6) the coil temperature (T coil ) of the magnetic coil (56) depending on the resistance specification. [2] Method according to claim 1, wherein the plurality of voltage pulses of the operating voltage correspond to a pulse-width modulated measuring voltage or a control pattern whose duty cycle is selected such that no movement or opening of the metering valve occurs. [3] The method of claim 2, wherein the current response corresponds to an effective coil current. [4] The method of claim 3, wherein the current response corresponds to an effective coil current after a predetermined period of time which is at least equal to the period of a transient response. [5] Method according to one of claims 1 to 4, wherein the coil temperature (T coil ) using a mapping function or a lookup table depending on the resistance specification (R coil ) is determined. [6] Method according to one of claims 1 to 4, wherein a temperature monitoring is carried out depending on the coil temperature (T coil ) is carried out. [7] Device for carrying out the method according to one of claims 1 to 6. [8] Reducing agent injection system (1) for injecting reducing agent into an exhaust tract (6) of an internal combustion engine, comprising: - a metering valve with a solenoid coil (56) for moving a valve pin (54) against a restoring force; - a device according to claim 7.

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