Fluid pump and method for stopping fluid pump

Abstract

The invention relates to a fluid pump (30), in particular a fluid pump (30) provided for conveying a reducing agent (8) in fluid form for reducing exhaust gases, comprising a pump chamber (32), a movable conveying element (34), a drive (40) for driving the conveying element (34), an actuatable inlet valve (44) and an actuatable outlet valve (48). The fluid pump (30) comprises a control device (54) which is designed to actuate the fluid pump (30) in such a way that an outflow valve (48) of the fluid pump (30) is opened during a discharge stroke of the conveying element (34); deactivating the drive (40) after opening the outflow valve (48); opening also an inflow valve (44) of the fluid pump (30) after deactivation of the drive (40) and thereby generating a hydraulic short circuit in the fluid pump (30), by means of which the fluid pressure in the pump chamber (32) is reduced; after a reduction in the fluid pressure in the pump chamber (32), the outflow valve (48) is closed and a drive (40) is activated in order to convey fluid remaining in the pump chamber (32) away from the pump chamber (32) through the inflow valve (44).

Description

Technical Field

[0001] The present invention relates to a method for stopping a fluid pump and a fluid pump configured to perform the method according to the present invention. Background Art

[0002] In order to reduce nitrogen oxides (NO x ) contained in the exhaust gas stream of an internal combustion engine, especially a diesel engine, in a so-called SCR system ("SCR" = "selective catalytic reduction"), an aqueous urea solution is injected as a liquid reducing agent into the exhaust system of the internal combustion engine.

[0003] The reducing agent is conveyed by a fluid delivery pump from a fluid tank to an injection device installed on the exhaust system of the internal combustion engine, and the reducing agent is injected into the exhaust system by the injection device.

[0004] A method for operating such a fluid delivery pump is described in the document DE 10 2019 219 635 A1.

[0005] The aqueous urea solution used as a reducing agent freezes at -11°C. Therefore, usually after the internal combustion engine is shut down, the SCR system is emptied as completely as possible to avoid frost damage caused by the freezing and subsequent expansion of the reducing agent. Summary of the Invention

[0006] The object of the present invention is to provide a method for stopping a fluid pump, which enables the fluid pump to be emptied as completely as possible when stopped. The object of the present invention is also to provide a fluid pump that can be emptied as completely as possible when deactivated or stopped.

[0007] The present invention includes a method for stopping a fluid pump, especially a fluid pump configured to convey a reducing agent in the form of a fluid to reduce exhaust gas. The fluid pump has a pump chamber, a movable conveying element, a driver for driving the conveying element, a controllable inlet valve, and a controllable outlet valve. The method according to the present invention includes: opening the inlet valve during the suction stroke of the conveying element to fill the pump chamber with fluid; then closing the inlet valve and opening the outlet valve during the discharge stroke of the conveying element; opening the inlet valve again at the end of the discharge stroke to create a hydraulic short circuit to reduce the fluid pressure in the pump chamber. After the fluid pressure in the pump chamber is reduced, closing the outlet valve and conveying the remaining fluid in the pump chamber through the inlet valve by driving the conveying element.

[0008] The invention further includes a fluid pump, in particular a fluid pump for conveying a reducing agent in fluid form to reduce exhaust gas, wherein the fluid pump has a pump chamber, a movable conveying element, a drive for driving the conveying element, a controllable inlet valve and a controllable outlet valve. The fluid pump according to the invention further includes a control device configured to control the fluid pump to stop in such a way that the inlet valve is opened during the discharge stroke of the conveying element to fill the pump chamber with fluid; then the inlet valve is closed and the outlet valve is opened during the discharge stroke of the conveying element; the inlet valve is opened again near the end of the discharge stroke, thereby creating a hydraulic short circuit to reduce the fluid pressure in the pump chamber. After the fluid pressure in the pump chamber is reduced, the outlet valve is closed and the remaining fluid in the pump chamber is conveyed out of the pump chamber through the inlet valve by driving the conveying element.

[0009] The fluid pump according to the invention can be almost completely emptied by performing the method according to the invention. In this way, the risk of frost damage caused by the freezing of the fluid in the fluid pump is significantly reduced.

[0010] By first opening the inlet valve when the drive is running, the pump chamber of the fluid pump is filled with fluid. Thereby, during the subsequent discharge stroke, the outlet valve can be assisted in opening by overcoming the outlet pressure with the overpressure generated in the pump chamber when the inlet valve is closed. The opening of the outlet valve assisted by the overpressure in the pump chamber results in that a smaller mechanical force must be applied to the outlet valve to open it. Therefore, the actuator provided for opening the outlet valve can be constructed more simply and at lower cost than an actuator that is not assisted by the overpressure generated in the pump chamber when opening the outlet valve.

[0011] In one embodiment, during the hydraulic short circuit (wherein both the inlet valve and the outlet valve are open), the drive is temporarily deactivated to provide more time for the pressure reduction.

[0012] If the pressure is reduced fast enough during the hydraulic short circuit, the temporary deactivation of the drive can be omitted.

[0013] In one embodiment, the method additionally includes: after the remaining fluid in the pump chamber is conveyed away from the pump chamber through the inlet valve, the inlet valve is closed and the drive is deactivated. By the negative pressure generated in the pump chamber after the inlet valve is closed, the conveying element is brought into the desired final position in this way. Therefore, the fluid pump can be brought into a defined stationary state in which the conveying element is in a pre-given position. Thus, the fluid pump can be started from a defined position when restarted.

[0014] In one embodiment, the inlet valve and the outlet valve are each electrically controllable such that they can be electrically opened and closed. The inlet valve and the outlet valve can in particular each have an electromagnetic coil and an armature, wherein the armature can be moved by energizing the electromagnetic coil in order to open or close the corresponding valve. Thus, the electrically controllable valves can be opened and closed in a targeted manner by appropriate electrical control in order to open and close the inlet or outlet of the fluid pump.

[0015] In one embodiment, the opening of the inlet valve includes a pulling-in phase (in which the armature is set in motion), a re-pulling-in phase after the pulling-in phase, and a holding phase (in which the valve remains in the open position). In particular, the current flowing through the inlet valve during the pulling-in phase, the re-pulling-in phase, and the holding phase can be of different magnitudes. In this way, the inlet valve can be opened particularly reliably and held in the open state.

[0016] In one embodiment, the opening of the outlet valve includes a pulling-in phase (in which the armature is set in motion), a re-pulling-in phase after the pulling-in phase, and a holding phase (in which the valve remains in the open position). In particular, the current flowing through the outlet valve during the pulling-in phase, the re-pulling-in phase, and the holding phase can be of different magnitudes. In this way, the outlet valve can be opened particularly reliably and held in the open state.

[0017] In one embodiment, the conveying element includes an elastic membrane that is movable in order to convey fluid. The elastic membrane has proven to be a conveying element for fluids, in particular for conveying a reducing agent in liquid form for exhaust gas aftertreatment. In an alternative embodiment, a piston can also be used as the conveying element instead of the elastic membrane.

[0018] In one embodiment, the conveying element is connected to the drive motor by a connecting rod in order to convert the rotational movement of the drive motor into an up-and-down movement of the conveying element. The drive motor can in particular be an electric motor.

[0019] The invention also includes a system for exhaust gas aftertreatment of an internal combustion engine, in particular a diesel engine, wherein the system includes a fluid tank for storing a reducing agent in fluid form; a metering valve configured to inject the reducing agent in fluid form into the exhaust system of the internal combustion engine; and a fluid pump according to the invention, which is configured to convey the reducing agent in fluid form from the fluid tank to the metering valve.

[0020] The invention also includes a motor vehicle having an internal combustion engine and a system for exhaust gas aftertreatment of the internal combustion engine according to the invention, wherein the system for exhaust gas aftertreatment includes a fluid pump according to the invention. Description of the Drawings

[0021] Embodiments of the invention are described below with reference to the drawings.

[0022] Figure 1 Schematic view of a motor vehicle having an internal combustion engine and a system for injecting a fluid reducing agent into the exhaust system of the internal combustion engine.

[0023] Figure 2 Schematic cross-sectional view of a fluid pump according to the invention.

[0024] Figure 3 Intuitive illustration of the control of the valve of the fluid pump when performing the method according to the invention. Detailed Description

[0025] Figure 1 Schematic view of a motor vehicle 1 having an internal combustion engine 4, in particular a diesel engine 4, and a system 2 for injecting a reducing agent in fluid form ("fluid") 8 stored in a fluid tank 6, in particular an aqueous urea solution into the exhaust system 10 of the internal combustion engine 4.

[0026] During operation of the system 2, the reducing agent 8 in fluid form is removed from the fluid tank 6 and supplied by a fluid pump 30 via a suitable pressure line 14 to an injection device 18 mounted on a metering connection 16 of the exhaust system 10. The injection device 18 injects the reducing agent 8 as a spray 20 into the exhaust system 10. In the exhaust system 10, the injected reducing agent 8 is mixed with the exhaust gas 22 flowing through the exhaust system 10 of the internal combustion engine 4 and reacts with the nitrogen oxides contained in the exhaust gas 22 in a catalytic converter 24 provided downstream of the injection device 20 in the exhaust system 10.

[0027] Figure 2 Schematic cross-sectional view of a fluid pump 30 according to the invention, which can be stopped by the method according to the invention.

[0028] The fluid pump 30 has a pump chamber 32 and a delivery element 34 configured as a movable membrane 34, which delimits the pump chamber 32 such that the volume of the pump chamber 32 is variable by the movement of the delivery element 34.

[0029] The delivery element 34 is eccentrically coupled to the rotor 38 of an electric motor 40 via a connecting rod 36. By operating the electric motor 40, the delivery element 34 can be placed in an oscillating up-and-down movement. Thus, the electric motor 40 serves as a drive for the delivery element 34.

[0030] The upward movement of the delivery element 34 corresponds to a suction stroke, during which the volume of the pump chamber 32 increases and the fluid 8 is sucked from the fluid tank 6 into the pump chamber 32.

[0031] The downward movement of the delivery element 34 corresponds to a discharge stroke, during which the volume of the pump chamber 32 decreases and the fluid 8 is discharged from the pump chamber 32 to the injection device 18.

[0032] In the inlet 42 of the fluid pump 30 (the inlet is connected to the Figure 2 An inlet valve 44 is configured in the outlet 46 of the fluid pump 30 (the outlet is fluidly connected to the fluid box 6 not shown in the figure). Figure 2 The injection device 18 (not shown) is fluidically connected to the outlet valve 48.

[0033] The inlet valve 44 and the outlet valve 48 each have an electromagnetic actuator 45 , 47 . The actuators 45 , 47 respectively actuate suitable sealing elements 50 , 52 in order to enable or block a flow through the inlet 42 or the outlet 46 .

[0034] The actuators 45 and 47 respectively have electromagnetic coils 45a and 47a and armatures 45b and 47b. The armatures 45b and 47b can be moved by energizing the coils 45a and 47a. The actuators 45 and 47 can be configured in particular so that the corresponding valves 44 and 48 are closed in a static state and opened by energizing the coils 45a and 47a of the corresponding actuators 45 and 47.

[0035] The fluid pump 30 also includes a control device 54 which is designed to control the electric motor 40 and the actuators 45 , 47 in order to start, operate and stop the fluid pump 30 .

[0036] The control device 54 is designed in particular to stop the fluid pump 30 in operation by carrying out the method according to the invention, which is described below with reference to Figure 3 to describe.

[0037] exist Figure 3 In the upper region of , the change of the current I (vertical axis) flowing through the electromagnetic coils 45a, 47a of the actuators 45, 47 over the time t (horizontal axis) is schematically plotted.

[0038] In this case, the current flowing through the inlet valve 44 formed in the inlet 42 is indicated by a solid line, and the current flowing through the outlet valve 48 formed in the outlet 46 is indicated by a dashed line.

[0039] exist Figure 3 The lower area of ? shows whether the electric motor 40 is switched on (“1”) or switched off (“0”).

[0040] After the last "normal" delivery stroke 71 is carried out (in which the inflow valve 44 has been opened to suck the fluid 8 from the fluid tank 6 into the pump chamber 32), at time point t1, the outflow valve 48 is opened during the discharge stroke of the delivery element 34. Here, the overpressure generated by the delivery element 34 in the discharge stroke in the pump chamber 32 assists the actuator 47 of the outflow valve 48 to overcome the fluid pressure in the outflow port 46 to open the sealing element 52 of the outflow valve 48. Therefore, the actuator 47 can be designed more simply and, in particular, only generate a relatively small force.

[0041] In the next step, the inflow valve 44 is also opened at time point t2>t1. The inflow valve 44 remains open here.

[0042] By opening the inflow valve 44 and the outflow valve 48 simultaneously, a so-called hydraulic short circuit is generated in the fluid pump 30, which enables the fluid pressure in the pump chamber 32 to be reduced.

[0043] The pressure reduction by the hydraulic short circuit is completed within 250 ms to 750 ms, in particular within approximately 500 ms.

[0044] During the hydraulic short circuit, the system pressure measured in the pressure line 14 or on the injection device 18 approximately corresponds to the fluid pressure in the pump chamber 32. Therefore, the fluid pressure in the pump chamber 32 can be approximately determined by measuring the system pressure.

[0045] During the hydraulic short circuit, the electric motor 40 can be deactivated within the time interval [t3, t4], as indicated by the dashed line in Figure 3 , such that the delivery element 34 is no longer actively driven by the electric motor 40. By temporarily deactivating the electric motor 40, additional time can be provided for the pressure reduction in the pump chamber 32 if needed.

[0046] If the pressure is reduced fast enough during the hydraulic short circuit, the temporary deactivation of the electric motor 40 can be omitted.

[0047] After the fluid pressure in the pump chamber 32 has been sufficiently reduced by the hydraulic short circuit, the outflow valve 48 is closed at time point t4. The electric motor 40 continues to run or is reactivated so as to convey the fluid 8 still remaining in the pump chamber 32 back to the fluid tank 6 through the always-open inflow valve 44 by the active movement of the delivery element 34.

[0048] At a subsequent time point t5>t4, the inflow valve 44 is also closed and the electric motor 40 is deactivated.

[0049] The lengths of the time intervals [t0, t1], [t0, t2] and [t4, t5] depend on the rotational speed of the electric motor 40. In a typical rotational speed range of 500 revolutions per minute to 1500 revolutions per minute, the length of the time interval [t0, t1] is in the range of 20 ms to 60 ms, the length of the time interval [t0, t2] is in the range of 40 ms to 120 ms, and the length of the time interval [t4, t5] is in the range of 20 ms to 60 ms.

[0050] When the volume of the pump chamber 32 increases during the suction stroke by the movement of the conveying element 34, a negative pressure generated in the pump chamber 32 during the closing of the valves 44, 48 and thus preventing pressure equalization with the inflow port 42 and / or the outflow port 46 moves the conveying element 34 into the desired final position, in which the negative pressure in the pump chamber 32 is minimal. As a result, the conveying element 34 of the fluid pump 30 is in a defined rest position near the bottom dead center.

[0051] This has the following advantages:

[0052] - The starting torque is reduced and thus the starting current required for driving during a restart of the fluid pump is reduced;

[0053] - The pressure peak in the pump chamber during the start of the fluid pump is reduced;

[0054] - The thawing time is shortened and the energy input required for thawing a frozen fluid pump is reduced;

[0055] - By maintaining the orientation of the rotor of the drive, the force acting on the conveying element is reduced, for example in a jammed state.

[0056] The targeted opening of the valves 44, 48 by energizing the coils 45a, 47a can respectively include an attraction phase 61, a re - attraction phase 62 and a holding phase 63.

[0057] In the attraction phase 61, a first voltage U is applied to the coils 45a, 47a of the corresponding actuators 45, 47 until the attraction current I is reached A . In the attraction phase 61, the coils 45a, 47a are especially energized continuously until the armatures 45b, 47b and the sealing elements 50, 52 coupled to the armatures 45b, 47b start to move.

[0058] After the armatures 45b, 47b and the sealing elements 50, 52 start to move, the coils 45a, 47a are energized again with the re - attraction current intensity I NA in the so - called re - attraction phase 62. The re - attraction phase 62 usually only lasts for a short moment and is set to ensure that the armatures 45b, 47b are firmly held in their open positions without bouncing back.

[0059] During the holding phase 63 after the re - closing phase 62, a so - called holding current I H flows through the corresponding coils 45a, 47a in order to reliably hold the sealing elements 50, 52 of the valves 44, 48 in the open state.

[0060] In order to close the corresponding valves 44, 48, the current I flowing through the coils 45a, 47a of the actuators 45, 47 is switched off. During the closing phase triggered by switching off the current I, the coils 45a, 47a discharge through a free - wheeling circuit or a free - wheeling diode ( Figure 2 not explicitly shown in the figure).

[0061] As shown in Figure 3 the current I flowing through the corresponding valves 44, 48 during the closing phase, re - closing phase and holding phase A 、I NA 、I H can be of different magnitudes. These currents are selected according to the respective circumstances in such a way that they ensure the reliable operation of the valves 44, 48.

Claims

1. A method for stopping a fluid pump (30), in particular a fluid pump (30) configured to convey a reducing agent (8) in fluid form for reducing exhaust gases, Among them, The fluid pump (30) has a pump chamber (32), a movable conveying element (34), a drive (40) for driving the conveying element (34), a controllable inlet valve (44) and a controllable outlet valve (48); And wherein the method comprises: Opening the inlet valve (44) during the suction stroke of the conveying element (34) in order to fill the pump chamber with fluid; Then closing the inlet valve (44); Opening the outlet valve (48) during the subsequent discharge stroke of the conveying element (34); Also opening the inlet valve (44) again and thereby creating a hydraulic short circuit in order to reduce the fluid pressure in the pump chamber (32); After the fluid pressure in the pump chamber (32) has been reduced, closing the outlet valve (48) and conveying the fluid remaining in the pump chamber (32) out of the pump chamber (32) through the inlet valve (44).

2. The method according to claim 1, wherein The method additionally comprises: after the reducing agent (8) in fluid form remaining in the pump chamber (32) has been conveyed out of the pump chamber (32) through the inlet valve (44), closing the inlet valve (44) and deactivating the drive (40), thereby bringing the conveying element (34) into a desired final position by the negative pressure generated in the pump chamber (32).

3. The method according to claim 1 or 2, Among them, The inlet valve (44) is electrically controllable, wherein the opening of the inlet valve (44) comprises a pulling-in phase (61), a re-pulling-in phase (62) and a holding phase (63), wherein the current flowing through the inlet valve (44) is of different magnitudes in the pulling-in phase (61), the re-pulling-in phase (62) and the holding phase (63), and / or wherein the outlet valve (48) is electrically controllable, wherein the opening of the outlet valve (48) comprises a pulling-in phase (61), a re-pulling-in phase (62) and a holding phase (63), wherein the current flowing through the outlet valve (48) is of different magnitudes in the pulling-in phase (61), the re-pulling-in phase (62) and the holding phase (63).

4. The method according to any one of claims 1 to 3, wherein, The method comprises temporarily deactivating the drive (40) during the hydraulic short circuit.

5. A fluid pump (30), in particular a fluid pump (30) for conveying a reducing agent (8) in fluid form for reducing exhaust gases, Among them, The fluid pump (30) has a pump chamber (32), a movable conveying element (34), a drive (40) for driving the conveying element (34), a controllable inlet valve (44) and a controllable outlet valve (48); and wherein the fluid pump (30) comprises a control device (54), the control device being configured to control the fluid pump (30) such that the inlet valve (44) is opened during the discharge stroke of the conveying element (34) in order to fill the pump chamber (32) with fluid; Close the inflow valve (44) and open the outflow valve (48) of the fluid pump (30) during the discharge stroke of the delivery element (34); After a certain time, open the inflow valve (44) of the fluid pump (30) again and thereby create a hydraulic short circuit in the fluid pump (30), through which the fluid pressure in the pump chamber (32) is reduced; After the fluid pressure in the pump chamber (32) has been reduced, close the outflow valve (48) and convey the fluid remaining in the pump chamber (32) away from the pump chamber (32) through the inflow valve (44).

6. The fluid pump (30) according to claim 5, wherein, The control device is additionally configured such that after the reducing agent (8) in the form of fluid remaining in the pump chamber (32) has been conveyed away from the pump chamber (32) through the inflow valve (44), the inflow valve (44) is closed and the drive (40) is deactivated, thereby bringing the delivery element (34) into the desired final position by the negative pressure generated in the pump chamber (32).

7. The fluid pump (30) according to claim 5 or 6, wherein, The delivery element (34) includes an elastic membrane, wherein the elastic membrane is connected to the drive (40), in particular an electric motor, in particular by means of a connecting rod (36).

8. The fluid pump (30) according to any one of claims 5 to 7, wherein, The inflow valve (44) and the outflow valve (48) each have an electrically controllable actuator (45, 47), wherein the actuators (45, 47) each have in particular an electric coil (45a, 47a) and an armature (45b, 47b), and the armature is movable by energizing the electric coil (45a, 47a).

9. A system (2) for post-treating the exhaust gas of an internal combustion engine (4), in particular a diesel engine, the system (2) comprising: - a fluid tank (6) for storing a reducing agent (8) in fluid form; - a metering valve (18) configured to inject the reducing agent (8) in fluid form into the exhaust system (10) of the internal combustion engine (4); and - a fluid pump (30) according to any one of claims 5 to 8, the fluid pump being configured to convey the reducing agent (8) in fluid form from the fluid tank (6) to the metering valve (18).

10. A motor vehicle (1) having an internal combustion engine (4) and a system (2) for post-treating the exhaust gas of the internal combustion engine (4) according to claim 9.

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