Patent Application
20190293189
The present invention concerns a stop valve. The invention furthermore concerns an SCR system which comprises this stop valve, and a method for detecting leaks and/or identifying variations in metered amounts in said SCR system. In addition, the present invention concerns a computer program which executes each step of the method when run on a computer device, and a machine-legible storage medium which stores the computer program. Finally, the invention concerns an electronic control unit which is configured to execute the method.
Stop valves are used to control movements of fluids. In open state, they predefine the flow direction of the fluid, and in closed state prevent the movement of the fluid. Stop valves are used today in SCR systems to control the movement of a reducing agent (AdBlue®). In particular, stop valves are arranged in a pressure line of the SCR system between a delivery module and a metering module. There they prevent a leakage of the reducing agent into the pressure line; otherwise, there is a possibility that this would freeze and damage sensitive components.
One example of a stop valve as described above is given in publication DE 10 2011 090 070 A1. This concerns a stop valve used in an SCR system. This is a 2/2-way directional control valve in which a diaphragm valve, by means of a diaphragm spring, is pressed onto a diaphragm. The passage state is controlled via a solenoid coil and can thus remain open automatically when the minimum pressure is achieved in the flow direction in the system. In closed state, or with the diaphragm valve closed, the stop valve prevents leakage.
Publication DE 10 2012 204 104 A1 also concerns a stop valve which is arranged in a device for purging an exhaust gas aftertreatment system. Here, the stop valve is arranged in a delivery line between the delivery module and the metering module. The 2/2-way valve is actuated hydraulically via an actuator, and therefore no magnet is required. A control line branches off the delivery line and is used to control the actuator. When, in delivery mode, a positive pressure prevails in the delivery line, the actuator is actuated and opens the valve.
Publication DE 10 2012 211 112 A1 also discloses a stop valve used in an SCR system. In this system, an additional switch valve ensures the switching between delivery mode and return mode. This stop valve consists of a changeover valve and a 2/2-way valve. The changeover valve opens the 2/2-way valve at two different pressure levels. As a result, the stop valve can be opened both in delivery mode and in return mode.
Publication DE 10 2012 209 689 A1 describes an arrangement for exhaust gas aftertreatment by means of SCR. Here, a delivery module and a stop valve are described. The stop valve prevents leakage by means of a shut-off element. This is achieved by a sealing ram which lies tightly on the sealing seat in closed state. The open state is achieved using a bistable spring element which presses the sealing ram against the contact face with low holding force. The bistable spring element here ensures a high closing force and a low holding force. This allows use of the valve without active deployment, so that the valve can be used preferably passively in this arrangement.
A stop valve is proposed which is configured to control a fluid movement. In particular, when it assumes a blocking mode, the stop valve prevents a movement of the fluid and a leakage. To this end it comprises a magnet yoke, a solenoid coil, a compression spring and a solenoid armature. The solenoid armature may in particular be configured as a flat armature or a solenoid plunger. An elastic membrane is arranged on the solenoid armature, wherein the membrane can be pressed with sealing effect onto at least one fluid connection. The compression spring is arranged on the solenoid armature such that it runs around the edge of the casing surface of the solenoid armature. In other words, the compression spring surrounds the solenoid armature on its inside. Also, the coil is arranged such that it is surrounded by the compression spring. The compression spring thus encloses both the solenoid armature and the coil. This prevents tilting of the solenoid armature and the stop valve requires no additional guide components.
According to one aspect, this stop valve is used in an SCR system. The SCR system comprises a pump in a delivery module and a metering module which are connected together by a pressure line. The stop valve described above is arranged in the pressure line. Furthermore, the pressure line comprises a pressure sensor which is arranged between the stop valve and the metering module. This SCR system has the advantage that a basic leakage through pump gaps of a pump, which can deliver and siphon back by changing its direction of rotation, is prevented.
The stop valve is preferably configured so that it can assume the following modes. In a blocking mode, the membrane is pressed by the solenoid armature onto both a fluid inlet and a fluid outlet, and closes both tightly. This offers the advantage that in blocking mode, the stop valve ensures blockage against reduced pressure and positive pressure both from the fluid inlet and from the fluid outlet. Furthermore, a metering mode is provided in which the stop valve is opened hydraulically unpowered above a set pressure, and remains open because of the pressure. This means that no active deployment and hence no permanent powering is required in metering mode of the SCR system. In addition, a return mode is provided in which a magnetic force between the magnet yoke and the solenoid armature holds the stop valve in an open position. This allows a reducing agent to be siphoned back out of the pressure line of the SCR system.
A further aspect of the stop valve concerns an ice pressure protection of the SCR system. The freezing reducing agent leads to an ice pressure which can cause displacement of a volume. The membrane may be pressed in the direction of the valve interior at the fluid inlet without the stop valve being opened. This defines an ice pressure displacement volume.
The method for detecting leaks and/or identifying variations in metered amounts is used in in the SCR system, including stop valve, as described above. Here, the method comprises the following steps. Firstly, the stop valve opens so that the pressure line can be filled with reducing agent. Then the stop valve is closed and a pressure downstream of the stop valve, i.e. between the stop valve and the metering module, is enclosed in the pressure line. The enclosed pressure is monitored by the pressure sensor. Now a pressure upstream of the stop valve, i.e. between the stop valve and the delivery module, is lowered by switching off the pump. In a further step, a leak detection and or identification of variations in metered amounts may be performed by monitoring the pressure downstream of the stop valve, as described above, by means of the pressure sensor.
Optionally, the stop valve may be closed by the spring force of the compression spring. This offers the advantage that the stop valve is closed automatically and also remains closed without the need for a power supply. The compression spring may also exert a force for pressing the membrane against a fluid inlet and a fluid outlet when the pressure is lowered upstream of the stop valve. In this way, simultaneous closure of both openings is achieved. This means that neither the reduced pressure from the pump upstream of the stop valve, nor the positive pressure from the enclosed pressure downstream of the stop valve, leads to an opening of the stop valve. Also, it is not necessary to supply the stop valve with power during leakage detection and/or identification of variations in metered amounts.
According to one aspect, when filling the pressure line with reducing agent, a first pressure is built up in the system. This lies in particular in a range between 5.8 bar and 10 bar. Then the pressure is reduced to a second pressure which in particular lies between 2 bar and 5.5 bar, whereupon the stop valve closes. This guarantees that the pressure throughout the SCR system is balanced. The pressure fall may be achieved for example via a choke or a check valve which connects a return with a portion of the pressure line upstream of the stop valve. The second pressure is thus enclosed in the pressure line between the stop valve and the metering module and may be used for leakage detection and/or identification of variations in metered quantities. Then, the pressure upstream of the stop valve is lowered to a third pressure of between 1 bar and 2 bar. This leads to a pressure difference between the fluid inlet and fluid outlet of the stop valve which causes a closure of the stop valve.
The leakage detection is preferably performed in that the enclosed pressure downstream of the stop valve (second pressure) is detected by the pressure sensor over a fixed time period from 0.5 to 30 seconds. If the enclosed pressure changes during this time period, a leakage in the pressure line or in the metering module can be concluded.
After leakage detection and/or identification of a variation in metered quantities, the pressure upstream of the stop valve, i.e. on the pump side, can again be increased to a fourth pressure. This may again lie in particular in a range between 4.8 bar and 10 bar. As a result, the SCR system is diagnosed and is suitable for metering.
The computer program is configured to perform each step of the method, in particular when executed on a computer or control unit. It allows implementation of the method in a conventional electronic control unit without the need to make structural changes thereto. For this, it is stored on the machine-legible storage medium.
By running the computer program on a conventional electronic control unit, the electronic control unit is obtained which is configured to perform a leakage detection and/or identification of variations in metered quantities.
Exemplary embodiments of the invention are shown in the drawings and explained in more detail in the description which follows.
The stop valve 100, depending on conditions or use, may assume different modes. In a blocking mode, the compression spring 107 presses the flat armature 105 in the direction of the fluid inlet 108 and the fluid outlet 109, so that the membrane 106 closes both simultaneously. Thus the stop valve 100 is closed by the spring force of the compression spring 107 and no power supply is required. This prevents a fluid from being able to flow through the stop valve. The spring force of the compression spring 107 also holds the stop valve closed if a reduced or positive pressure is present at the fluid inlet 108 and/or fluid outlet 109, as long as this is sufficiently low, for example below 5.6 bar.
A further mode allows the fluid to flow from the fluid inlet to the fluid outlet. In this metering mode, a pressure p prevails in the fluid inlet 108 which presses against the membrane 106 and hence against the flat armature 105, and is sufficiently great that this overcomes the spring force of the compression spring 107. Thus the flat armature 105 is pressed in the direction of the magnet yoke 101, and a connection is created between the fluid inlet 108 and the fluid outlet 109. In the present exemplary embodiment, this pressure p amounts to 5.6 bar. In this mode too, no power supply is required. The membrane opens with the support of the pressure, and when a pressure p of 4 to 10 bar is present in the system, offers no pressure loss.
In addition, the stop valve 100 may assume a return mode by actuation of the solenoid coil 102. This provides a magnetic force between the magnet yoke 101 and the flat armature 105, which means that the flat armature 105 is drawn towards the magnet yoke 101 and the spring force of the compression spring 107 is overcome. Thus a connection is created or maintained between the fluid outlet 109 and the fluid inlet 108, through which the fluid can flow.
Since the membrane 106 is elastic, it is possible to deform this. Therefore, at the fluid inlet, it is possible to press the membrane 106 into the interior of the stop valve between the flat armature 105 and the magnet housing 104. However, in blocking mode, the membrane 106 still closes both the fluid inlet 108 and the fluid outlet 109. For this reason, only an additional volume is formed. This volume may be used if the fluid is a liquid which expands on freezing, in that it functions as an ice pressure displacement volume.
A further step 305 follows in which a leakage is detected and/or a variation in metered quantities is identified. In leakage detection, the pressure p2 enclosed in the second portion 242 of the pressure line 240 is observed over a predefined period of 10 seconds. If the pressure p falls during the observed period, some of the fluid must be escaping through one of the components of the metering module 230, pressure line 240, stop valve 100 or connecting pieces in between. Since the stop valve 100 is configured to prevent a leakage as far as possible, a leakage from the metering valve 230 and/or the pressure line 240 can be detected from this. Furthermore, via the pressure and the delivered quantity of reducing agent, a discrepancy between a desired metering quantity and the actual metering quantity, which is enclosed in the second portion 242 of the pressure line 240, can be identified.
After the leakage has been detected and/or the variation in metered quantities identified, in a further step 306 the pressure p in the first portion 241 of the pressure line 240 is increased again in that the pump 211 is switched on again. When the pressure p reaches a fourth pressure p4, the stop valve 100 opens 307 again and the system is diagnosed and capable of metering.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2016 208 600.6 | May 2016 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/057075 | 3/24/2017 | WO | 00 |
