Method and device for emptying injection system for injecting reducing agent when engine is shut down
By determining the compression modulus of the injection system before the engine is turned off and precisely controlling the reducing agent discharge amount, the problems of freezing damage and prolonging start time of the injection system are solved, and the rapid recovery and anti-freeze protection of the system are achieved.
Patent Information
- Application Number
- CN202510159108.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-02-16
- Filing Date
- 2025-02-13
- Publication Date
- 2025-08-19
AI Technical Summary
When the engine is turned off, it is difficult for the prior art to effectively emptiate the reducing agent in the injection system, resulting in freezing damage and an extended pressure setting time at the next engine start.
By determining the compression modulus of the injection system before the engine is turned off, the discharge amount of reducing agent is accurately controlled, which is divided into pressure reduction, pre-emption and emptiation stages. The mapping function is used to adjust the duration of each stage to ensure that the appropriate amount of reducing agent is retained in the injection system to prevent freezing and reduce start-up time.
Effectively prevents the injection system from freezing and damage, and shortens the pressure setting time at the next engine start.
Smart Images
Figure CN120506299A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to an exhaust gas aftertreatment system for an internal combustion engine, into which a reducing agent is injected by means of an injection system for reducing nitrogen oxides. The invention also relates to measures for emptying the injection system when the engine is switched off. Background Art
[0002] When shutting down an engine system comprising an internal combustion engine and an exhaust gas aftertreatment system, the exhaust gas aftertreatment system must be placed in a state in which it is protected from freezing damage at low temperatures and in which exhaust gas aftertreatment can be restored as quickly as possible upon the next engine start. Therefore, it is fundamentally important for the shutdown procedure that, on the one hand, the injection valves of the injection system are kept as free of reducing agent as possible to prevent freezing damage, and, on the other hand, that the pressure build-up time after the next engine start is minimized to enable the injection system to enter an operating state as quickly as possible. This is achieved by retaining a certain amount of reducing agent in the delivery system after the engine is shut down. Summary of the Invention
[0003] According to the present invention, a method and a corresponding device are provided for purging a reducing agent injection system of an exhaust gas aftertreatment device of an engine system after an engine shutdown.
[0004] Additional configurations are given below.
[0005] According to a first aspect, a method for operating a reducing agent injection system of an exhaust gas aftertreatment device of an engine system is provided, in particular an at least partially computer-implemented method, comprising the following steps:
[0006] - after confirming that the engine is stopped, the reducing agent is discharged from the pressure line in a series of pressure reduction phases, pre-emptying phases and emptying phases;
[0007] determining the compressibility modulus of the reducing agent-filled pressure line of the reducing agent injection system immediately before (e.g. between 0 and 0.5 seconds), during or after (e.g. between 0 and 0.5 seconds) an engine stop;
[0008] - determining the amount of reducing agent discharged during the pressure reduction phase based on the compression modulus;
[0009] - running a pre-emptying phase and / or an emptying phase as a function of the amount of reducing agent discharged, in order to set a predetermined residual amount of reducing agent in the pressure line.
[0010] When the engine is shut down, the reducing agent must be removed from the injection system to prevent damage to the injection system in the event of freezing. Typically, after the engine is stopped, the injection system is emptied in three stages: a pressure reduction phase, a pre-emptying phase, and an emptying phase. During these three stages, the reducing agent is returned to the reducing agent tank.
[0011] However, when the engine is stopped, a defined amount of reducing agent must remain in the injection system so that the required pressure can be built up as quickly as possible when the engine is next started. Therefore, the more reducing agent is removed from the injection system, the longer it takes for the pressure to build up when the engine is next started.
[0012] Furthermore, in the pressure reduction phase, the return valve can be opened with the metering valve closed in order to reduce the pressure in the pressure line, in particular to between 0 and 1 bar, in particular between 0.3 and 0.7 bar, by discharging the reducing agent into the reducing agent tank, wherein, in the pre-emptying phase, with the metering valve closed, a negative pressure is generated in the pressure line by means of a reducing agent pump, in that the reducing agent is pumped back into the reducing agent tank, the reducing agent pump being operated in reverse, wherein, in the emptying phase, the metering valve is opened so that the reducing agent returns from the metering valve into the reducing agent tank.
[0013] The shutdown procedure first includes a pressure reduction phase. With the injection valve closed, this phase is performed by opening the reducing agent pump for return flow to reduce the pressure in the reducing agent line to between 0 and 1 bar, in particular between 0.3 and 0.7 bar. This pressure reduction phase typically lasts until the pressure in the pressure line approaches ambient pressure. The amount of recirculating reducing agent is usually not measured. The pressure reduction phase continues until the pressure is almost completely released.
[0014] Subsequently, during the pre-emptying phase, a negative pressure is generated in the injection system by means of the reducing agent pump, which is running in reverse. The metering valve remains closed until a predetermined time has elapsed or a defined negative pressure value has been reached. The negative pressure is generated by pumping out the reducing agent. Typically, this process is time-controlled, so that the pre-emptying phase ends after the predetermined time has elapsed or a defined negative pressure value has been reached.
[0015] Subsequently, during the draining phase, the metering valve is opened, allowing the reducing agent to be returned from the metering valve to the reducing agent tank at a defined mass flow rate. In all steps, a defined amount of reducing agent is returned to the reducing agent tank. The amount of returning reducing agent is determined, in particular during the pressure reduction phase, by the injection system and the compressibility of the reducing agent. The draining phase can also be controlled by time or the number of pump cycles.
[0016] The compressibility modulus is a property that describes the stiffness of the medium in the reductant line of the injection system and the surrounding structure that defines the volume of the reductant line. The compressibility modulus is also affected by the amount of gas bubbles. Therefore, the compressibility modulus determined before the engine is stopped indicates how much reductant is returned to the reductant tank during the pressure reduction phase.
[0017] If air bubbles are present in the reducing agent in the reducing agent line, they act as additional pressure buffers and significantly change the compressibility of the entire system. The more air bubbles there are in the reducing agent, the more reducing agent will be discharged via backflow during the pressure reduction phase when the reducing agent pump is switched on. Since the emptying of the injection system is usually time-controlled, the amount of reducing agent discharged during the pressure reduction phase and pre-emptying phase is higher. Therefore, it is impossible to accurately determine the amount of reducing agent discharged from the reducing agent line. To accurately determine the amount of reducing agent to be discharged, it is necessary to know the compressibility of the entire reducing agent injection system, which takes the presence of air bubbles into account.
[0018] Provision can be made for the pre-emptying phase and / or the emptying phase to be carried out for a predetermined duration, which depends on the amount of reducing agent discharged during the pressure reduction phase. If the pre-emptying and emptying phases are run in a time-controlled manner, the compression modulus largely determines the amount of reducing agent remaining in the pressure line after the pressure reduction phase and the amount of reducing agent that can subsequently be returned to the reducing agent tank. The duration of the pre-emptying and emptying phases can be adjusted depending on the amount of reducing agent discharged during the pressure reduction phase.
[0019] The compression modulus can be determined by first determining the air fraction in the pressure line and mapping the value of the compression modulus in relation to the air fraction according to a predetermined mapping function.
[0020] Furthermore, the compression modulus may be determined based on a pressure change and a volume change of the pressure line during a pump stroke of the reductant pump before the engine is stopped.
[0021] The control is carried out in such a way that not all the reducing agent is removed from the injection system. The amount of reducing agent discharged is determined by time control. Furthermore, the compression modulus of the injection system and the arrangement of the reducing agent primarily determines the amount of reducing agent discharged. If air bubbles are present in the reducing agent in the pressure line during the emptying and pre-emptying phases, the compression modulus can change significantly, and more reducing agent than is necessary to prevent freezing damage can be removed from the pressure line during the pressure reduction phase. Consequently, the time required to establish operational readiness after engine start-up is unnecessarily prolonged, as it takes longer to establish the reducing agent pressure required to put the exhaust gas aftertreatment system into operation.
[0022] The method thus provides for determining the compression modulus for the injection system at the moment of engine stop in order to better determine the amount of reducing agent discharged into the reducing agent tank during the pressure reduction phase. This makes it possible to determine the amount of reducing agent discharged and to time the pre-draining phase and the draining phase so that the desired amount of reducing agent is removed from the injection system.
[0023] The compression modulus K corresponds to the stiffness of the system and characterizes the system's behavior with respect to its volume and pressure, K=Δp / ΔV·V, where Δp denotes the pressure difference in the pressure line before and after a pump stroke (plunger pump), the pressure difference being measured or modeled by a sensor, ΔV denotes the volume change, which corresponds to the volume delivered by the reducing agent pump during one pump cycle, and V denotes the base volume of the pressure line that can be filled with reducing agent.
[0024] The compressibility modulus K is also directly coupled to the frequency and the speed of sound α of the hydraulic system of the injection system, where ρ corresponds to the density of the reducing agent.
[0025] Furthermore, there's a correlation between the speed of sound, a, and the resonant frequency of the injection system: f = α / (2·L), where L corresponds to the length of the reductant line pressure pipe or the length of the pressure wave path within the injection system. This illustrates the relationship between the speed of sound and the frequency of the pressure waves in the system. Monitoring the frequency can be another method for determining system stiffness.
[0026] In order to determine the amount of reducing agent discharged during the pressure reduction phase, a mapping function or a mapping table can be used based on the previously determined compression modulus. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The following describes the embodiments in detail with reference to the accompanying drawings.
[0028] Figure 1 A schematic diagram of an injection system for an exhaust gas aftertreatment device of an engine system;
[0029] Figure 2 A flow chart illustrating a method of operating an injection system while the engine is stopped. DETAILED DESCRIPTION
[0030] Figure 1 A schematic diagram illustrates a reducing agent injection system 1 for an exhaust gas aftertreatment device of an internal combustion engine system. Reducing agent injection system 1 is used to inject reducing agent into an exhaust pipe 2 of the engine system to reduce nitrogen oxides in the combustion exhaust gas of the internal combustion engine. Reducing agent injection system 1 is operated to controllably introduce a predetermined amount of reducing agent into the exhaust gas stream via a control unit 10.
[0031] The reducing agent injection system 1 includes a device for providing a reducing agent (such as a urea aqueous solution (Ad )) of a reducing agent tank 3, a supply module 4 with a reducing agent pump 41, a pressure sensor 42 for measuring the reducing agent pressure in a pressure line 5 and a pressure buffer 43, a pressure line 5 and an injection unit 6 with at least one metering valve 61.
[0032] The reducing agent pump 41 is used to deliver the reducing agent from the reducing agent tank 3 to the pressure line 5 to provide the reducing agent at a predetermined pressure. The required amount of reducing agent specified by the control unit is injected into the mixing chamber of the exhaust pipe 2 through the metering valve 61.
[0033] To prevent freezing damage and to enable a rapid pressure buildup after the next engine start, provision is made to remove a defined amount of reducing agent from the pressure line 5 when the engine is stopped. Since the discharge of reducing agent depends significantly on the rigidity of the system, the exact amount of reducing agent cannot be determined using a time-controlled method for discharging reducing agent. Therefore, provision is made to first determine the amount of discharged reducing agent using the compression modulus.
[0034] To do this, perform the following steps when the engine is stopped: Figure 2 The flowchart describes the method in detail.
[0035] In step S1, it is first checked whether a request or signal for stopping the engine has been issued. If an engine stop or a request for stopping the engine is detected, the method proceeds to step S2. Otherwise (alternative solution: no), the method jumps back to step S1.
[0036] In step S2, the engine system is stopped.
[0037] In step S3 , before, during or after the engine stop, in particular when an engine stop signal has been issued, the compression modulus K is determined based on the pressure change Δp of the reducing agent in the pressure line before and after a piston stroke of the reducing agent pump and the volume change ΔV of the reducing agent pump during the last or additionally triggered pump stroke, as measured by the pressure sensor 42 :
[0038] K = ΔP / ΔV·V.
[0039] V corresponds to the volume of the pressure line 5 , a portion within the injection unit and the volume of the reducing agent pump.
[0040] In step S4, the reducing agent pump 4 for return flow is turned on to reduce the pressure in the pressure line 5 and remove a certain amount of reducing agent from the pressure line 5, as pressure equalization is achieved between the reducing agent system and the ambient pressure. This pressure reduction phase continues until the pressure drops to the ambient pressure and thus achieves pressure equalization with the pressure in the reducing agent tank 3.
[0041] The amount of reducing agent expelled during this pressure reduction phase cannot be measured directly, but can be estimated based on the stiffness of the injection system 1. The stiffness of the injection system 1 is represented by the compression modulus. In step S5, the amount of reducing agent expelled during the pressure reduction phase is determined based on the compression modulus using a predefined mapping function.
[0042] In the subsequent pre-emptying phase, in step S6, the reducing agent is conveyed back into the reducing agent tank 3 by means of the reducing agent pump, with the metering valve 61 remaining closed. This generates a negative pressure in the reducing agent line 5. The pre-emptying phase is carried out in a time-controlled manner. The duration of the pre-emptying phase is determined based on the previously determined amount of discharged reducing agent, in particular by applying a mapping function.
[0043] In the subsequent emptying phase, in step S7, the metering valve 61 is opened so that the reducing agent pump can convey reducing agent from the pressure line 5 into the reducing agent tank 3. During the emptying phase, the reducing agent pump conveys reducing agent back into the reducing agent tank. The duration of the active emptying phase is determined based on the previously determined amount of discharged reducing agent, in particular by applying another mapping function.
Claims
1. A method, in particular a computer-implemented method, for operating a reducing agent injection system (1) of an exhaust gas aftertreatment device of an engine system, the reducing agent injection system having at least one metering valve (61), the method comprising the following steps: - after confirming the engine stop or detecting a signal of said engine stop (S1), discharging (S3) the reducing agent from the pressure line (5) in a succession of pressure reduction phases, pre-emptying phases and emptying phases; - determining the compressibility modulus (K) of the pressure line (5) of the reducing agent injection system (1) filled with reducing agent immediately before, during or after stopping the engine; - determining the amount of reducing agent discharged during the pressure reduction phase as a function of the compression modulus (K); - the pre-emptying phase and / or the emptying phase is run as a function of the amount of reducing agent discharged, in order to set a predetermined residual amount of reducing agent in the pressure line (5).
2. The method according to claim 1, wherein In the pressure reduction phase, the reducing agent pump (4) is opened for return flow (S4) when the metering valve (61) is closed, so that the pressure in the pressure line is reduced to between 0 and 1 bar, in particular between 0.3 and 0.7 bar, by discharging the reducing agent into the reducing agent tank (3), wherein, in the pre-emptying phase, a negative pressure (S6) is generated in the pressure line by means of the reducing agent pump (4) when the metering valve (61) is closed, in that the reducing agent is pumped back into the reducing agent tank (3), the reducing agent pump running in reverse, wherein, in the emptying phase, the metering valve (61) is opened (S7) so that the reducing agent flows back from the metering valve (61) into the reducing agent tank (3).
3. The method according to claim 1 or 2, wherein: The pre-emptying phase and / or the emptying phase is carried out for a predetermined duration which depends on the amount of reducing agent discharged during the pressure reduction phase.
4. The method according to claim 3, wherein: The compression modulus (K) is determined by first determining the air fraction in the pressure line (5) and mapping the value of the compression modulus (K) in association with the air fraction according to a predetermined mapping function.
5. The method according to claim 3, wherein The compression modulus (K) is determined based on a pressure change and a volume change of the pressure line (5) during one pump stroke of the reducing agent pump (4) immediately before the engine is stopped. 6 . A device configured to carry out the method according to claim 1 . 7 . A computer program configured to implement the method according to claim 1 .
8. A machine-readable storage medium having stored thereon the computer program according to claim 7.