Patent Application
20140331647
The present invention relates to a method pertaining to an SCR system. The invention relates also to a computer program product comprising program code for a computer for implementing a method according to the invention. The invention relates also to an SCR system and a motor vehicle equipped with the SCR system.
Vehicles today use, for example, urea as reductant in SCR (selective catalytic reduction) systems which comprise an SCR catalyst in which said reductant and NOx gas can react and be converted to nitrogen gas and water. Various types of reductants may be used in SCR systems. AdBlue is an example of a commonly used reductant.
One type of SCR system comprises a container which holds a reductant. The SCR system has also a pump arranged to draw said reductant from the container via a suction hose and supply it via a pressure hose to a dosing unit situated adjacent to an exhaust system of the vehicle, e.g. adjacent to an exhaust pipe of the exhaust system. The dosing unit is arranged to inject a necessary amount of reductant into an exhaust system upstream of the SCR catalyst according to operating routines which are stored in a control unit of the vehicle.
There is a constant need to reduce the amount of emissions from engines of motor vehicles, not least in the case of heavy vehicles such as trucks and buses, in the light of continually tighter legal requirements for ever smaller emissions.
There are various ways of reducing emissions from motor vehicles
US2011239625 describes a device for injecting reducing agent in an exhaust system. The specification is concerned with ensuring that reducing agent dosage is correct and is adjusted on the basis inter alia of surrounding pressure. A specified pressure is set which depends on surrounding pressure and the reducing agent dosage is controlled by setting the length of time when the dosing valve is open.
US2011232267 describes a method and a device for dosing of reducing agent in an exhaust system. The reducing agent has to be added to the exhaust system in an evenly divided form. A desired drop size is determined on the basis of at least one exhaust parameter, followed by setting a pressure as a function of the desired drop size. The exhaust parameters on which the desired drop size is based comprise at least one from among volumetric flow, flow velocity, mass flow, gas temperature and gas pressure.
WO2006050318 describes a method and a device for dosing of reducing agent in an exhaust system. To adapt the reducing agent dosage to all operating situations it is also possible to add vaporised reducing agent to the engine. The amount of reducing agent dosed is based on a predetermined optimised amount of reducing agent, the temperature of the exhaust gases and how the engine is running.
US2005235632 describes a device and a method for injecting a reducing agent into an exhaust flow in order to reduce emissions from an engine. To achieve as small drops as possible, a swirl plate [0013] is used. To inject a certain amount of reducing agent which depends on the engine's speed, the temperature of the exhaust gases, exhaust flow, exhaust pressure, when the engine fuel supply takes place and desired NOx reduction, the dosage is controlled by adjusting the length of time when the injection takes place, i.e. the time when the valve (22) in the dosing unit 16 is open, at a predetermined specified pressure of the reducing agent.
EP1291498 describes a device for controlling emissions from an engine by injecting a fuel in an exhaust system. The fuel is injected in the form of drops of controlled size. Their diameter is determined on the basis of the temperature of the exhaust gases or on the basis of the temperature in the middle of the catalyst. To control the dosage, an electronic control unit (ECU) controls the amount of reducing agent which is to be supplied.
US2009301067 describes a device for reducing agent dosing into an exhaust flow of a combustion engine, which takes place according to two different schemes depending on the engine's operating state.
There is a constant need to improve today's SCR systems in order to reduce the amount of undesirable emissions from a combustion engine.
One object of the present invention is to propose a novel and advantageous method for improving the performance of an SCR system.
Another object of the invention is to propose a novel and advantageous SCR system and a novel and advantageous computer program for improving the performance of an SCR system.
One object of the present invention is to propose a novel and advantageous method for reducing the amount of undesirable emissions from a combustion engine.
A further object of the invention is to propose an alternative method pertaining to an SCR system, and an alternative computer program pertaining to an SCR system and an alternative SCR system.
These objects are achieved with a method pertaining to SCR systems for a motor vehicle according to the invention.
One aspect of the invention proposes a method pertaining to SCR systems for a motor vehicle, comprising a feed device to feed reducing agent from a container to a dosing unit for supply of said reducing agent to an exhaust duct of the vehicle. The method comprises the step of controlling the dosing unit's dosage by means of a pressure at which reducing agent is dosed.
One aspect of the invention proposes a method pertaining to SCR systems for a motor vehicle, comprising a feed device to feed reducing agent from a container to a dosing unit for supply of said reducing agent to an exhaust duct of the vehicle. The method comprises the step of controlling the dosing unit's dosage by means of a pressure at which reducing agent is dosed, which pressure is controlled by control of a rotation speed of said feed device.
Flexible dosing of reducing agent in an SCR system is thus made possible. A relatively high working pressure of said reducing agent generally results in a drop size distribution with more smaller drops which can more readily be captured in an exhaust flow from the vehicle's engine. A relatively low working pressure of said reducing agent may generally result in a drop size distribution with more larger drops with a higher kinetic energy which are not affected by the exhaust flow in the same way as smaller drops. Smaller drops are advantageous in certain operating situations, e.g. at lower exhaust temperatures a smaller drop may vaporise relatively quickly in the exhaust flow. In another operating situation where a large amount of thermal energy is stored in the exhaust system, larger drops are advantageous in that they can for example be directed towards a surface of the exhaust system. Varying drop sizes are advantageous in certain cases where certain drops vaporise relatively quickly in the exhaust flow and other drops are for example directed towards various surfaces in the exhaust system. This results in improved performance of the SCR system.
By suitably varying the working pressure according to the invention, e.g. on the basis of inherent characteristics of the dosing unit, it is possible with advantage to alter in desirable ways a cone angle for the reductant dosed. In an analogous way this may be employed to optimise the pattern of encounter between and/or mixing of reducing agent and exhaust gases. By altering a working pressure of the SCR system it is also possible to influence the velocity of the reducing agent drops. This results in substantially the same advantages as described above.
The dosing unit may be configured to comprise an aperture and a needle. The needle covers the aperture when the dosing unit is not dosing reducing agent in the exhaust duct. For reducing agent dosing, the needle moves away from the aperture, allowing the reducing agent to be dosed in the exhaust duct. The needle may be used to adjust the degree of opening of the dosing unit. The dosing unit may alternatively comprise an aperture of adjustable size to be further able to control the reducing agent dosage. As a further alternative, the aperture may be directionable for further potential control of the dosing of the reducing agent into the exhaust duct.
The method may comprise the step of controlling the dosing unit's dosage by means of the pressure on the basis of a prevailing temperature of a surface or component of said exhaust duct.
Controlling the dosing unit's dosage by means of the pressure at which reducing agent is dosed thus makes it possible to influence an associated drop size distribution. This may greatly affect a degree of conversion of NOx in the SCR catalyst.
The method may comprise the step of controlling the pressure at which reducing agent is dosed by controlling a rotation speed of said feed device. This results in an accurate method pertaining to an SCR system according to one aspect of the invention. Said speed may be controlled with very great accuracy, making it possible for a working pressure of said reducing agent in the SCR system to be also controlled with great accuracy.
In one aspect of the present invention, the pressure may be varied during an opening phase of the dosing unit. This may be advantageous in that the drop size distribution of the reducing agent at the beginning and end of an opening phase of the dosing unit, with a constant pressure of the reducing agent, may differ from the drop size distribution during the remainder of the opening phase. The drop size distribution throughout the opening phase may be controlled by varying the pressure during it. In certain operating situations it is desirable to have a uniform drop size distribution throughout the opening phase, which may be achieved by applying a certain pressure at the beginning and end of an opening phase and a different pressure during the remainder of the opening phase. In certain operating situations it may be desirable for more larger or smaller drops of reducing agent to be dosed at the beginning than at the end of the opening phase. Alternatively, the pressure during an opening phase may be kept constant but vary between opening phases.
In one version the method may comprise the step of controlling the pressure at which reducing agent is dosed by controlling a displacement of a piston pump incorporated in said dosing unit.
The dosing unit may take the form of any desired pump, e.g. a diaphragm pump or a gearwheel pump.
The method may comprise the step of controlling the pressure by altering a constriction in a reducing agent feedback line from the dosing unit to said container. This results in an accurate method pertaining to an SCR system according to one aspect of the invention. Said constriction may be altered with very great accuracy, making it also possible for a working pressure of the SCR system to be controlled with great accuracy. A robust method may thus reliably be achieved.
In one embodiment example a pressure of said reducing agent may be controlled by controlling not only a rotation speed of said dosing unit but also a constriction in a reducing agent feedback line from the dosing unit to said container. The result is an accurate method pertaining to an SCR system according to one aspect of the invention whereby advantageous synergy effects are achieved. Simultaneously controlling both a rotation speed of said dosing unit and altering said constriction makes it possible for the pressure to build up quickly.
The method may comprise the step of controlling the pressure by altering the configuration of the dosing unit, resulting in an accurate method pertaining to an SCR system according to one aspect of the invention. Said configuration may be altered with very great accuracy, making it also possible for a working pressure of the SCR system to be controlled with great accuracy. A robust method may thus reliably be achieved.
The method may comprise the step of controlling the dosing unit's dosage by means of the pressure on the basis of a prevailing temperature of a surface in the exhaust system. It may comprise the step of controlling the dosing unit's dosage by means of the pressure on the basis of a prevailing temperature of a surface in the exhaust system where reducing agent dosed vaporises. It may comprise the step of controlling the dosing unit's dosage by means of the pressure on the basis of a prevailing temperature of a suitable surface in the exhaust system. It may comprise the step of controlling the dosing unit's dosage by means of the pressure on the basis of a prevailing temperature of a suitable component of the exhaust system, e.g. a vaporisation module, a particle filter or said SCR catalyst. Improved performance of the SCR system may thus be achieved.
Said surface may comprise various parts of the exhaust system where the reducing agent vaporises. It may for example be a surface towards which the dosing unit's nozzle is directed in the exhaust system. It may also be a surface downstream of the dosing unit where reducing agent is carried by the exhaust flow. It may be a surface of a vaporisation unit situated downstream of the dosing unit in the exhaust system. It may be a surface which reducing agent dosed encounters.
The temperature of said surface or component may be detected by means of a temperature sensor situated at or close to said surface where the reducing agent vaporises. The temperature of said surface or component may be detected by a temperature sensor situated on or in the immediate vicinity of said surface where the reducing agent vaporises. In certain cases it is advantageous to have a sensor on an outside surface of the exhaust system to prevent sensor wear. In certain cases this temperature is that of an inside surface of the exhaust system. In other cases the temperature of said inside surface may be calculated on the basis of a measured temperature of the outside surface. Alternatively, a prevailing temperature of said inside surface may be calculated on the basis of other parameters, e.g. prevailing temperature of an exhaust flow from an engine, prevailing mass flow of exhaust gases from an engine, amount of reducing agent dosed and the characteristics and state of the reducing agent, e.g. its chemical composition and prevailing temperature at the time of dosing.
The method may comprise the step of controlling the dosing unit's dosage by means of the pressure on the basis of a prevailing temperature of an exhaust flow from an engine and/or a prevailing mass flow of exhaust gases from an engine. Improved performance of the SCR system may thus be achieved. A versatile method pertaining to an SCR system is thus also achieved, since alternative versions are possible. A prevailing mass flow of the exhaust gases may be calculated by a control unit of the vehicle, e.g. using the engine's air intake and fuel intake as parameters. Alternatively, the mass flow of the exhaust gases may be measured by means of a mass flow sensor. As temperature sensors are relatively inexpensive, a cost-effective method is also achieved according to one aspect of the invention.
The method may comprise the step of controlling the dosing unit's dosage by means of the pressure on the basis of a prevailing temperature of a surface in an exhaust pipe of the vehicle.
The method may comprise the step of controlling the dosing unit's dosage by means of the pressure on the basis of a prevailing temperature of air surrounding the vehicle. This entails having to install temperature sensors on the vehicle in a suitable way if none has already been installed.
The method may comprise the step of controlling the dosing unit's dosage by means of the pressure on the basis of previous operating situations of the vehicle. This entails a control unit of the vehicle using calculations according to a stored model as a basis for controlling the dosing unit's dosage in a suitable way by means of the pressure.
The method may comprise the step of controlling the dosing unit's dosage by means of the pressure and a dosing cycle rate, resulting in a method pertaining to an SCR system with improved performance. Combined control of the dosing unit's dosage by means of the pressure of the reductant during dosing and making changes to a prevailing cycle rate of the SCR system makes it possible to achieve an optimised spray pattern of said reducing agent dosed. The cycle rate may for example be within a range of 1-10 Hz. During a cycle, the dosing unit's opening period may be determined to regulate the amount of reducing agent dosed during said cycle. The amount of undesirable emissions from the vehicle's engine may thus be advantageously reduced.
The method may comprise the step of varying the pressure of the reductant within a range of 1-15 bar. In one version the method may comprise the step of varying the pressure of the reductant within a range of 7-13 bar. In one version the method may comprise the step of varying the pressure of the reductant within a range of 10-50 bar. In one version the method may comprise the step of varying the pressure of the reductant within a range of 100-300 bar. In one version the method may comprise the step of varying the pressure of the reductant within any suitable range. The result is a robust method whereby a working range is defined beforehand, eliminating risks of undesirable spray patterns caused by too low or too high working pressure. An operationally safe and reliable method pertaining to an SCR system is thus achieved according to one aspect of the present invention.
The method may comprise the step of varying the pressure of the reductant steplessly during said control of the dosing unit's dosage, thus achieving a method whereby a desired spray pattern of said reductant may be set in a well-defined way. A method for an SCR system whereby a desired mixture of exhaust gases and reducing agent may be set with very great accuracy is thus advantageously achieved.
The method may further comprise the step of varying the pressure of the reductant, in discrete steps during said control of the dosing unit's dosage, resulting in a method for an SCR system which involves relatively simple programming routines. Providing control of the dosing unit's dosage on the basis of discrete settable steps of the working pressure makes it possible for a rotation speed of the feed device to be directed towards predetermined set-point values, affording the advantage of data processing which involves fewer calculations.
The method may comprise the step of altering a dosing cycle rate steplessly, resulting in a method whereby a desired spray pattern of said reductant may be set in a well-defined way. A method pertaining to an SCR system whereby a desired mixture of exhaust gases and reducing agent may be set with very great accuracy is thus advantageously achieved.
The method may comprise the step of altering a dosing cycle rate in discrete steps during said control of the dosing unit's dosage. Providing control of the dosing unit's dosage on the basis of discrete settable steps of the cycle rate makes it possible for a rotation speed of the feed device to be directed towards predetermined set-point values, affording the advantage of data processing which involves fewer calculations.
The method may comprise the step of controlling the dosing unit's dosage by means of the pressure of the reductant and a dosing cycle rate on the basis of a prevailing exhaust temperature and/or a prevailing mass flow of exhaust gases from an engine of the vehicle.
It should be noted that the method may incorporate one or more of the above features in suitable combinations.
The method is easy to implement in existing motor vehicles. Software pertaining to an SCR system according to the invention may be installed in a control unit of the vehicle during the manufacture of the vehicle. A purchaser of the vehicle may thus have the possibility of selecting the function of the method as an option.
Software which comprises program code for an SCR system according to the invention will be easy to update or replace. Moreover, different parts of the software which contain the program code may be replaced independently of one another. This modular configuration is advantageous from a maintenance perspective.
One aspect of the invention proposes an SCR system for a motor vehicle, comprising a feed device to feed reducing agent from a container to a dosing unit for supply of said reducing agent to an exhaust duct of the vehicle, comprising means for controlling the dosing unit's dosage by means of a pressure at which reducing agent is dosed, and means for controlling the pressure by control of a rotation speed of said feed device.
One aspect of the invention proposes an SCR system for a motor vehicle, comprising a feed device to feed reducing agent from a container to a dosing unit for supply of said reducing agent to an exhaust duct of the vehicle. The SCR system comprises means for controlling the dosing unit's dosage by means of a pressure at which reducing agent is dosed.
The SCR system may further comprise means for controlling the pressure by control of a rotation speed of said feed device.
The SCR system may comprise means for controlling the dosing unit's dosage by means of the pressure on the basis of a prevailing temperature of a surface or component of said exhaust duct.
The SCR system may comprise means for determining a prevailing temperature of a surface or component of said exhaust duct.
The SCR system may comprise means for controlling the pressure by altering a constriction in a reducing agent feedback line from the dosing unit to said container.
The SCR system may comprise means for controlling the pressure by altering the configuration of the dosing unit.
The SCR system may comprise means for controlling the dosing unit's dosage by means of the pressure on the basis of a prevailing temperature of a surface in the exhaust system.
The SCR system may further comprise means for detecting a prevailing temperature of a surface in the exhaust system. It may comprise means for determining a prevailing temperature of a surface in the exhaust system. It may comprise means for determining a prevailing temperature of a surface in an exhaust duct which is provided to lead exhaust gases from an engine to the surroundings.
The SCR system may comprise means for determining a prevailing temperature of a silencer of an exhaust system. It may comprise means for determining a prevailing temperature of a suitable component of a silencer of an exhaust system.
The SCR system may comprise means for calculating a prevailing temperature of a suitable surface in the exhaust system. It may comprise means for calculating a prevailing temperature of a surface in the exhaust system where reducing agent dosed at least partly vaporises. Said calculation may be based on specified parameters, e.g. exhaust mass flow and exhaust temperature.
The SCR system may comprise means for controlling the dosing unit's dosage by means of the pressure on the basis of a prevailing temperature of an exhaust flow from an engine and/or a prevailing mass flow of exhaust gases from an engine.
The SCR system may further comprise means for controlling the dosing unit's dosage by means of the pressure and a dosing cycle rate.
The SCR system may further comprise means for varying the pressure of the reductant within a range of 5-15 bar.
The SCR system may comprise means for varying the pressure of the reductant steplessly during said control of the dosing unit's dosage.
The SCR system may comprise means for varying the pressure of the reductant in discrete steps during said control of the dosing unit's dosage.
The SCR system may comprise means for altering a dosing cycle rate steplessly or in discrete steps during said control of the dosing unit's dosage.
The SCR system may comprise means for controlling the dosing unit's dosage by means of the pressure of the reductant and a dosing cycle rate on the basis of a prevailing exhaust temperature and/or a prevailing mass flow of exhaust gases from an engine of the vehicle.
The above objects are also achieved with a motor vehicle which is provided with the SCR system. The vehicle may be a truck, bus or car.
One aspect of the invention is a proposed computer program for an SCR system, which program comprises program code stored on a computer-readable medium for causing an electronic control unit or another computer connected to the electronic control unit to perform steps according to the invention.
One aspect of the invention is a proposed computer program for an SCR system, which program comprises program code for causing an electronic control unit or another computer connected to the electronic control unit to perform steps according to the invention.
One aspect of the invention is a proposed computer program for an SCR system, which program comprises program code stored on a medium for causing an electronic control unit or another computer connected to the electronic control unit to perform steps according to the invention.
One aspect of the invention is a proposed computer program product comprising a program code stored on a computer-readable medium for performing method steps according to the invention when said computer program is run on an electronic control unit or another computer connected to the electronic control unit.
Further objects, advantages and novel features of the present invention will become apparent to one skilled in the art from the following details, and also by putting the invention into practice. Whereas the invention is described below, it should be noted that it is not confined to the specific details described. One skilled in the art having access to the teachings herein will recognise further applications, modifications and incorporations within other fields, which are within the scope of the invention.
For fuller understanding of the present invention and its further objects and advantages, the detailed description set out below should be read in conjunction with the accompanying drawings, in which the same reference notations pertain to similar items in the various diagrams and
a is a schematic flowchart of a method according to an embodiment of the invention,
b is a more detailed schematic flowchart of a method according to an embodiment of the invention, and
It should be noted that the invention is suitable for application in any SCR system and is therefore not confined to SCR systems for motor vehicles. The innovative method and the innovative SCR system according to one aspect of the invention are well suited to other platforms which comprise an SCR system than motor vehicles, e.g. watercraft. The watercraft may be of any kind, e.g. motorboats, steamers, ferries or ships.
The innovative method and the innovative SCR system according to one aspect of the invention are for example also well suited to systems which comprise industrial engines and/or engine-powered industrial robots.
The innovative method and the innovative SCR system according to one aspect of the invention are also well suited to various kinds of power plants, e.g. an electric power plant provided with a diesel generator.
The innovative method and the innovative SCR system are well suited to any engine system which comprises an engine and an SCR system, e.g. on a locomotive or some other platform.
The innovative method and the innovative SCR system are well suited to any system which comprises an NOx generator and an SCR system.
The term “link” refers herein to a communication link which may be a physical connection such as an opto-electronic communication line, or a non-physical connection such as a wireless connection, e.g. a radio link or microwave link.
The term “line” refers herein to a passage for holding and conveying a fluid, e.g. a reducing agent in liquid form. The line may be a pipe of any size and be made of any suitable material, e.g. plastic, rubber or metal.
The term “reductant” or “reducing agent” refers herein to an agent used for reacting with certain emissions in an SCR system. These emissions may for example be NOx gas. The terms “reductant” and “reducing agent” are herein used synonymously. In one version, said reductant is so-called AdBlue. Other kinds of reductants may of course be used. AdBlue is herein cited as an example of a reductant, but one skilled in the art will appreciate that the innovative method and the innovative device are feasible with other types of reductants, subject to necessary adaptations, in control algorithms in accordance with the innovative method.
The term “cycle rate” refers herein to a rate defined by the number of dosing periods, also called dosing cycles, per second. It should however be noted that at least one active dose of reducing agent from the dosing unit may take place during a dosing cycle.
The term “pressure of the reductant” refers herein to a pressure at which said reductant is dosed from a dosing unit of the innovative SCR system. The pressure at which said reductant is dosed, and the working pressure Pr, are herein used synonymously.
A first line 271 is provided to lead the reductant to a pump 230 from the container 205. The pump 230 may be any suitable pump. It may be a diaphragm pump with at least one filter. It may be arranged to be driven by an electric motor (not depicted). The pump is adapted to drawing the reductant from the container 205 via the first line 271 and supplying it via a second line 272 to a dosing unit 250. The dosing unit comprises an electrically controlled dosing device by means of which a flow of reductant added to the exhaust system can be controlled. The dosing unit comprises an electrically controlled dosing valve by means of which a flow of reductant added to the exhaust system can be controlled. The pump is adapted to pressurising the reductant in the second line 272. The dosing unit is provided with a throttle unit, which may also be called throttle valve, against which said pressure of the reductant may build up in the subsystem 299. This pressure is herein referred to as the working pressure Pr of the SCR system. Said throttle unit may be of a fixed or adjustable type.
The dosing unit 250 is adapted to supplying said reductant to an exhaust system of the vehicle 100. More specifically, it is adapted to supplying a suitable amount of reductant in a controlled way to an exhaust duct 290 of the vehicle 100. In this version, an SCR catalyst (not depicted) is situated downstream of a location in the exhaust system where the supply of reductant takes place. The amount of reductant supplied in the exhaust system is intended to be used in the SCR catalyst for reducing the amount of unacceptable emissions.
The dosing unit 250 may be situated adjacent to said exhaust duct 290 which is provided to lead exhaust gases from a combustion engine (not depicted) of the vehicle to the SCR catalyst and thence to the vehicle's surroundings. A third line 273 running between the dosing unit 250 and the container 205 is adapted to leading back to the container a certain amount of the reductant fed to the dosing valve 250. This configuration results in advantageous cooling of the dosing unit 250. The dosing unit is thus cooled by a flow of the reductant when it is pumped through it from the pump 230 to the container 205.
A first control unit 200 is arranged for communication with a pressure sensor 220 via a link 221. This pressure sensor is adapted to detecting a prevailing pressure Pr of the reductant at the location where the sensor is fitted. In this version the sensor is situated adjacent to the second line 272 to measure the working pressure Pr of the reductant downstream of the pump 230. In another version it is situated in the dosing unit 250 to measure the working pressure Pr of the reductant downstream of the pump. It is adapted to continuously sending signals via the link 221 to the first control unit 200 which contain information about a prevailing pressure Pr of the reductant.
The first control unit 200 is arranged for communication with the pump 230 via a link 231 and is adapted to controlling the operation of the pump. In one example the first control unit is adapted to controlling the pump by means of an electric motor. The first control unit is adapted to influencing the working pressure Pr in the second line 272, which may be achieved in various suitable ways.
In one example, the first control unit 200 is adapted to altering a prevailing rotation speed RPM of the pump 230, making it possible for the pressure Pr to be altered in desirable ways. It may be raised by increasing the speed of the pump. It may be lowered by reducing the speed of the pump.
In another example, the first control unit 200 may be adapted to influencing the pressure Pr by controlling a change in the stroke length of a piston or a diaphragm of the pump 230. By altering an internal configuration or internal geometry of the pump it is also possible for the pressure Pr to be varied while maintaining a substantially constant speed RPM of the pump. The pressure may thus for example be influenced by altering a stroke length of pistons or diaphragms of the pump.
The first control unit 200 is arranged for communication with a first temperature sensor 240 via a link 241. This sensor is adapted to detecting a prevailing temperature T1 of an exhaust flow from the vehicle's engine. In one example this first sensor is situated immediately downstream of the vehicle's engine and upstream of a dosing unit 250. It is adapted to continuously detecting a prevailing temperature T1 of the exhaust flow and sending signals which contain information about said prevailing temperature to the first control unit via the link 241.
The first control unit 200 is arranged for communication with a second temperature sensor 260 via a link 261. This sensor is adapted to detecting a prevailing temperature T2 of a surface in the exhaust system where the reducing agent vaporises. In one example this second sensor is situated directly downstream of a dosing unit 250. In another example it is situated in a vaporisation unit 270 downstream of the dosing unit. This second sensor is adapted to continuously detecting a prevailing temperature T2 of a surface and sending signals which contain information about said temperature to the first control unit via the link 261.
The first control unit 200 is arranged for communication with the dosing unit 250 via a link 251 and is adapted to controlling the operation of the dosing unit, e.g. in order to regulate the supply of reductant to the vehicle's exhaust system.
The dosing unit 250 may be provided with a nozzle to dose the reductant for mixing with exhaust gases in an exhaust system of the vehicle. In one version a geometry of said nozzle may be variable, making it possible to control the pressure Pr of the reductant. The first control unit 200 is adapted to altering said variable configuration of the dosing unit in order to control the pressure Pr of the reductant.
The first control unit 200 is adapted in one version to using the signals received from the pressure sensor 220 which contain information about a prevailing pressure of the reductant as a basis for running said pump 230 in a manner in accordance of one aspect of the innovative method. Feedback control of the working pressure Pr is thus achieved.
The first control unit 200 is adapted to calculating an exhaust mass flow MF of the exhaust gases from the vehicle's engine. It is adapted to continuously determining an exhaust mass flow MF of the exhaust gases from the vehicle's engine. This may be achieved in any suitable way.
In one version the subsystem comprises a mass flow sensor (not depicted) adapted to continuously measuring a prevailing exhaust mass flow from the vehicle's engine. Said sensor is adapted to continuously sending signals which contain information about a prevailing exhaust mass flow to the first control unit via a link.
The first control unit 200 is adapted to controlling the dosage of the dosing unit 250 by means of a pressure Pr at which reducing agent is dosed. It may be adapted to controlling the pressure Pr by control of the speed RPM of the pump 230. It may be adapted to controlling the pressure Pr by altering a constriction in the line 273 for reducing agent from the dosing unit 250 to the container 205. In one alternative, the first control unit is adapted to controlling the pressure Pr by altering a constriction of reducing agent flow in the dosing unit 250, which flow is intended to lead to the container 205. It may be adapted to controlling the pressure Pr by altering the configuration of the dosing device of the dosing unit. It may adapted to controlling the dosing unit's dosage by means of the pressure Pr on the basis of a prevailing temperature T1 of an exhaust flow from an engine and/or a prevailing mass flow MF of exhaust gases from an engine. It may be adapted to controlling the dosing unit's dosage by means of the pressure Pr of the reductant and a dosing cycle rate CF. It may be adapted to varying the pressure Pr of the reductant within a range of 5-15 bar. It may be adapted to varying the pressure Pr of the reductant steplessly during said control of the dosing unit's dosage. It may be adapted to varying the pressure Pr of the reductant in discrete steps during said control of the dosing unit's dosage. It may be adapted to altering a dosing cycle rate CF steplessly or in discrete steps during said control of the dosing unit's dosage. It may adapted to controlling the dosing unit's dosage by means of the pressure Pr of the reductant and a dosing cycle rate CF on the basis of a prevailing exhaust temperature T1 and/or a prevailing exhaust mass flow MF of exhaust gases from an engine of the vehicle. It is adapted to controlling the dosing unit's dosage by means of a pressure Pr at which reducing agent is dosed, which pressure is controlled by control of a speed (RPM) of said feed device 230. The first control unit is adapted to controlling the dosing unit's dosage by means of the pressure on the basis of a prevailing temperature T2 of a surface or component of said exhaust duct 290.
A second control unit 210 is arranged for communication with the first control unit 200 via a link 201. This second control unit may be detachably connected to the first control unit. It may be a control unit external to the vehicle. It may be adapted to conducting the innovative method steps according to the invention. It may be used to cross-load software to the first control unit, particularly software for applying the innovative method. It may alternatively be arranged for communication with the first control unit via an internal network of the vehicle. It may be adapted to performing functions substantially similar to the first control unit, e.g. controlling the dosing unit's dosage by means of a pressure Pr at which reducing agent is dosed. The innovative method may be conducted by the first control unit 200 or the second control unit 210 or by both of them.
Some examples appear below of how the working pressure Pr may be controlled by the first control unit 200 in various different operating situations of the vehicle 100.
A change from a reference state to a state with higher exhaust temperature T and greater exhaust mass flow MF (e.g. T>400 degrees C. and MF>1000 kg/h) is here determined. The working pressure Pr is thus lowered (e.g. from 9 to 5 bar) to achieve dosage in larger drops of reducing agent which may be directed better in the large exhaust flow and encounter desired warm surface in the vehicle's exhaust system. Controlled wall encounter is thus advantageously achieved.
A change from a reference state to a state with higher exhaust temperature T and smaller exhaust mass flow (e.g. T>400 degrees C. and MF<1000 kg/h) is here determined. The working pressure Pr is thus raised (e.g. from 9 to 15 bar) to achieve dosage in smaller drops of reducing agent which may vaporise immediately in the exhaust flow before they encounter a surface in the vehicle's exhaust system. Improved vaporisation of reducing agent before wall encounter is thus advantageously achieved.
A change from a reference state to a state with lower exhaust temperature T and greater exhaust mass flow MF (e.g. T<250 degrees C. and MF>1000 kg/h) is here determined. The working pressure Pr may here be kept at a reference level (e.g. 9 bar) to achieve a drop size distribution which comprises both large and small drops of reducing agent. This means that certain drops may be entrained by the exhaust flow while others may be directed by the flow. A large encounter surface in the vehicle's exhaust system is thus achieved for best possible utilisation of thermal energy available therein and prevention of local cooling.
A change from a reference state to a state with lower exhaust temperature T and smaller exhaust mass flow MF (e.g. T<250 degrees C. and MF<1000 kg/h) is here determined. The working pressure Pr may here be raised to achieve small drops which may vaporise more quickly on the surfaces encountered in the exhaust system or may actually vaporise in the exhaust flow. The result is rapid vaporisation in the exhaust and/or on surfaces in the exhaust system when this operating situation has least thermal energy available for vaporisation of said reducing agent.
In a case of transient operation, the method may be supplemented so that control is based on a preceding operating situation. In one example after a lengthy period of operation with relatively high exhaust temperature T and a relative large exhaust flow the vehicle's exhaust system may still be warm despite a prevailing exhaust mass flow and a prevailing exhaust temperature both being low at the time. A corresponding earlier prevailing working pressure may thus with advantage continue to be utilised for an appropriate period of time.
In one aspect of the invention the working pressure Pr may be controlled on the basis of a change in a detected exhaust backpressure of the vehicle. In response to an increase in such a backpressure the working pressure may with advantage be raised in a suitable way to maintain a desired spray pattern of reducing agent dosed.
In one aspect of the invention the working pressure Pr may be controlled on the basis of a prevailing temperature of air surrounding the vehicle.
In a situation where the temperature of the surrounding air is below 0 degrees C. the working pressure may be raised as appropriate, e.g. by 2 bar, to alter the drop size distribution towards smaller drops and thus potentially facilitate vaporisation of reducing agent dosed.
In one aspect of the invention the working pressure Pr may be controlled on the basis of a prevailing temperature of the reducing agent in the vehicle's SCR system.
In a situation where the prevailing temperature of the reducing agent is for example above 50 degrees C., the working pressure may be lowered as appropriate, e.g. by 2 bar, to compensate for a faster vaporisation rate caused by the warm reducing agent.
a is a schematic flowchart of a method pertaining to SCR systems for a motor vehicle, comprising a feed device to feed reducing agent from a container to a dosing unit for supply of said reducing agent to an exhaust duct of the vehicle, according to an embodiment of the invention. The method comprises a first step s301 comprising the step of controlling the dosing unit's dosage by means of a pressure at which reducing agent is dosed. The method ends after step s301.
b is a schematic flowchart of a method pertaining to SCR systems for a motor vehicle, comprising a feed device to feed reducing agent from a container to a dosing unit for supply of said reducing agent to an exhaust duct of the vehicle, according to an embodiment of the invention.
The method comprises a first step s310 comprising the step of determining a prevailing temperature T1 of exhaust gases from the engine of the vehicle 100. This may be effected by means of the temperature sensor 240. Step s310 is followed by a step s320.
Method step s320 comprises the step of determining a prevailing mass flow MF of said exhaust gases. This exhaust mass flow may in one example be calculated by the first control unit 200. Alternatively it may be detected by means of suitable sensors or equipment. Step s320 is followed by a step s330.
Method step s330 comprises the step of controlling the dosage of the dosing unit 250 by means of a pressure Pr at which reducing agent is dosed. This pressure may be altered by influencing a speed of the pump 230. It may alternatively or in combination be altered by acting upon a constriction in the line 273. It may alternatively or in combination be altered by altering the configuration of the dosing unit's dosing device.
In one version, the dosage of the dosing unit 250 is controlled by means of the pressure Pr on the basis of a said prevailing temperature T1 determined of the exhaust flow and/or on the basis of said prevailing exhaust mass flow MF determined.
Step s330 is followed by a step s340.
Method step s340 comprises the step of controlling the dosage of the dosing unit 250 by means of a cycle rate of the SCR system. In one version said control of the dosing unit's dosage is by means of the pressure Pr at which reducing agent is dosed, at the same time as said control of the dosing unit's dosage by means of a cycle rate of the SCR system.
In one version, the dosage of the dosing unit 250 is controlled by means of the pressure Pr of the reductant and by means of a dosing cycle rate CF at the same time on the basis of said prevailing exhaust temperature T1 determined and/or said prevailing exhaust mass flow MF determined.
The method ends after step s340.
A proposed computer program P comprises routines for controlling the dosage of the dosing unit 250 by means of a pressure Pr at which reducing agent is dosed. The program comprises routines for controlling the pressure Pr by control of the speed RPM of the pump 230. The program comprises routines for controlling the pressure Pr by altering a constriction in the line 273 for reducing agent from the dosing unit 250 to the container 205. In one alternative, the program comprises routines for controlling the pressure Pr by altering a constriction of reducing agent flow in the dosing unit, which flow is intended to lead to the container. The program comprises routines for controlling the pressure Pr by altering the configuration of the dosing device of the dosing unit. The program comprises routines for controlling the dosing unit's dosage by means of the pressure Pr on the basis of a prevailing temperature T of an exhaust flow from an engine and/or a prevailing mass flow MF of exhaust gases from an engine. The program comprises routines for controlling the dosing unit's dosage by means of the pressure Pr of the reductant and a dosing cycle rate CF. The program comprises routines for varying the pressure Pr of the reductant within a range of [5, 15] bar. The program comprises routines for varying the pressure Pr of the reductant steplessly during said control of the dosing unit's dosage. The program comprises routines for varying the pressure Pr of the reductant in discrete steps during said control of the dosing unit's dosage. The program comprises routines for altering a dosing cycle rate CF steplessly or in discrete steps during said control of the dosing unit's dosage. The program comprises routines for controlling the dosing unit's dosage by means of the pressure Pr of the reductant and a dosing cycle rate CF on the basis of a prevailing exhaust temperature T and/or a prevailing exhaust mass flow MF of exhaust gases from an engine of the vehicle. The program comprises routines for controlling the dosing unit's dosage by means of a pressure Pr at which reducing agent is dosed, which pressure is controlled by control of a speed (RPM) of said feed device 230. The program comprises routines for controlling the dosing unit's dosage by means of the pressure on the basis of a prevailing temperature T2 of a surface or component of said exhaust duct 290.
The program P may be stored in an executable form or in compressed form in a memory 460 and/or in a read/write memory 450.
Where the data processing unit 410 is described as performing a certain function, it means that the data processing unit conducts a certain part of the program stored in the memory 460, or a certain part of the program stored in the read/write memory 450.
The data processing device 410 can communicate with a data port 499 via a data bus 415. The non-volatile memory 420 is intended for communication with the data processing unit 410 via a data bus 412. The separate memory 460 is intended to communicate with the data processing unit 410 via a data bus 411. The read/write memory 450 is adapted to communicating with the data processing unit via a data bus 414. The data port 499 may for example have the links 201, 221, 231, 241 and 251 connected to it (see
When data are received on the data port 499, they are temporarily stored in the second memory element 440. When input data have been stored temporarily, the data processing unit 410 is prepared to effect code execution as described above. In one version, signals received on the data port 499 contain information about a prevailing working pressure Pr of the reductant in the SCR system. In one version, signals received on the data port contain information about a prevailing temperature T1 of the exhaust gases in an exhaust system of the vehicle. In one version, signals received on the data port contain information about a prevailing mass flow MF of the exhaust gases in an exhaust system of the vehicle.
The signals received on the data port 499 may be used by the device 400 to apply the herein innovative method.
Parts of the methods herein described may be conducted by the device 400 by means of the data processing unit 410 which runs the program stored in the memory 460 or the read/write memory 450. When the device 400 runs the program, methods herein described are executed.
The foregoing description of the preferred embodiments of the present invention is provided for illustrative and descriptive purposes. It is not intended to be exhaustive nor to restrict the invention to the variants described. Many modifications and variations will obviously suggest themselves to one skilled in the art. The embodiments have been chosen and described in order best to explain the principles of the invention and their practical applications and hence make it possible for one skilled in the art to understand the invention for different embodiments and with the various modifications appropriate to the intended use.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1151192-0 | Dec 2011 | SE | national |
| 1251409-7 | Dec 2012 | SE | national |
The present application is a 35 U.S.C. §§371 national phase conversion of PCT/SE2012/051367, filed Dec. 10, 2012, which claims priority of Swedish Patent Application No. 1151192-0, filed 14 Dec. 2011 and Swedish Patent Application No. 1251409-7, filed 12 Dec. 2012, the contents of which are incorporated by reference herein. The PCT International Application was published in the English language.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE2012/051378 | 12/12/2012 | WO | 00 | 6/13/2014 |
