DE102009029188A1 - dosing - Google Patents

Abstract

The dosing system is connected with a fuel injection system, which is formed for injecting fuel under pressure into a combustion chamber. The dosing system comprises a pumping unit (4), which is hydraulically connected with the fuel injection system, such that the fluid is injected into the exhaust tract by pressure produced in the fuel injection system.

Description

State of the art

The invention relates to a metering system for injecting a fluid into an exhaust line of an internal combustion engine.

It is known to inject a urea solution into the exhaust gas tract of the internal combustion engine for selective catalytic reduction (SCR) of nitrogen oxides of an internal combustion engine, in particular of a diesel engine. Due to the interaction of the urea with the hot exhaust gases, ammonia gas develops which, in the presence of a catalyst arranged in the exhaust gas line, reacts with the nitrogen oxides in the exhaust gas stream.

There are various ways to inject the urea solution into the exhaust system. So it is known to spray the urea solution by means of compressed air into the exhaust system. The urea solution can be very finely atomized with the help of compressed air. Since compressed air must be provided for such a method, the realization is complicated and expensive.

In an alternative metering system, an injection pressure is generated by means of a mechanical pump, which is, for example, electrically driven, and the pressurized urea solution is injected into the exhaust gas line by means of an electrically controlled injector. In this method, the injector heats up strongly and must be cooled by cooling fins or an internal cooling circuit in order to operate trouble-free even at high exhaust gas temperatures. The necessary cooling also makes such a dosing system consuming and expensive.

Disclosure of the invention

An object of the invention is to provide an improved metering system for injecting a fluid into an exhaust line of an internal combustion engine, which is reliable, low maintenance and cost feasible.

The object is achieved by an inventive dosing according to independent claim 1. The dependent claims describe advantageous embodiments of a metering system according to the invention.

A metering system according to the invention for injecting a fluid into an exhaust line of an internal combustion engine connected to a fuel injection system configured to pressurize and inject fuel into at least one combustion chamber of the internal combustion engine comprises a pumping device configured and hydraulically connected to the pump Fuel injection system is connected, that the fluid can be injected by the pressure generated in the fuel injection system in the exhaust line.

Such a metering system does not require its own electrically or mechanically driven pump because the fuel injection pressure generated in the existing fuel injection system is used to generate the injection pressure through which the fluid is injected into the exhaust line. An inventive dosing is therefore much simpler structure than the previously known fluid injection systems that are operated with an additional electric pump or compressed air. The pump in the fuel injection system is due to the good lubricating properties of the fuel, such. As diesel fuel, much easier executable as a pump for media without lubricating properties, such. As aqueous urea solutions.

The use of a common, possibly larger-sized, pump for the fuel injection system and the metering system is also favorable from an energetic point of view, since a common larger pump can be operated with a higher efficiency than two separate, correspondingly smaller-sized pumps. This is especially true when the fuel injection pump is electrically powered and the pumping power is adaptable to the need.

In one embodiment, the fuel injection system has a low-pressure region with a delivery pressure generated by a prefeed pump, which is designed, for example, as a gear pump, in the range from 5 to 10 bar, in particular 6 bar, and a high-pressure region in which a high fuel pressure generated by a high-pressure pump from up to several hundred bar prevails. An inventive metering system is advantageously coupled to the low-pressure region of the fuel injection system, since the low pressure of up to 10 bar for injecting the fluid into the exhaust line is sufficient and a pumping device in the low pressure range is easier and less expensive to implement than in the high pressure area.

In one embodiment, the pumping device is a diaphragm pump having two chambers separated by a movable diaphragm. The volume of the two chambers is variable by moving the membrane, wherein an increase in the volume of the first chamber leads to a corresponding reduction in the volume of the second chamber and vice versa. By means of such a diaphragm pump, a coupling of the fuel injection system with the metering system can be realized simply and inexpensively.

In one embodiment, the first chamber is hydraulically connected to the fuel injection system and the second chamber is hydraulically connected to a fluid tank and a fluid injector. As a result, fluid can be pressurized from the fluid tank by utilizing the pressure prevailing in the fuel injection system and supplied to the fluid injector. By the fluid injection member, the fluid is injected into the exhaust line.

With such an arrangement, the fluid can be injected into the exhaust line without the need for an additional electrically or mechanically driven pumping device. The fluid injector can be designed, in particular, as a pressure wave-controlled fluid injector which does not have its own actuator system. Such a pressure wave-controlled fluid injector is particularly robust and requires no active or passive cooling. A metering system with a pressure wave-controlled fluid injector is therefore particularly cost feasible.

In one embodiment, the pump device is hydraulically connected to the fuel injection system via a changeover valve. By suitable control of the switching valve, the amount of injected into the exhaust line fluid is adjustable.

In one embodiment, the diaphragm pump additionally includes at least one piston configured to apply a force to the diaphragm. Thereby, the pressure exerted on the fluid in the diaphragm pump pressure can be increased, whereby a larger amount of fluid can be injected into the exhaust system in a short time.

In one embodiment, the piston is movably disposed between a low pressure stage and a high pressure stage. The high pressure stage is hydraulically connected to the fuel injection system so that the piston is movable by the pressure generated in the fuel injection system. The piston allows the fluid to be put under increased pressure particularly effectively.

In one embodiment, a fuel bore is formed in the piston, which connects the high-pressure stage hydraulically with the first chamber of the diaphragm pump. By such a bore, the first chamber is easily filled with fuel from the high pressure stage. A diaphragm pump with such a piston is particularly simple and inexpensive to implement.

In one embodiment, a return element is provided in the diaphragm pump, which is designed to exert a restoring force on the piston. As a result, the piston can be moved back into the starting position particularly quickly, so that the diaphragm pump can be operated at a high frequency.

In one embodiment, at least one stop element is provided in the diaphragm pump, which is designed to limit the piston stroke. By such a stop element damage to the diaphragm pump is avoided by an uncontrolled striking the piston. By selecting a correspondingly sized stop element, the delivery volume of the diaphragm pump can be adjusted, whereby an exact dosage of the funded by the diaphragm pump fluid is possible.

The invention will be explained in more detail below with reference to the accompanying figures. Showing:

1 a schematic representation of a first embodiment of a metering system according to the invention;

2 a schematic representation of a second embodiment of a metering system according to the invention; and

3 an alternative embodiment of a pump device according to the invention.

1 shows a first embodiment of a metering system according to the invention for injecting a fluid into the exhaust line of an internal combustion engine in a schematic representation.

An internal combustion engine, not shown, is connected to a fuel injection system configured to inject fuel into at least one combustion chamber of the internal combustion engine.

The fuel injection system includes a fuel tank 46 on. A prefeed pump 30 removed via a sampling line 28 Fuel from the fuel tank 46 and puts the fuel under an elevated but relatively low pressure of up to 10 bar. In the fuel line 29 at the outlet of the pre-feed pump 30 is attached, is a pressure sensor 32 provided to that of the prefeed pump 30 monitor generated pressure. The fuel flows out of the pre-feed pump 30 in a metering unit 34 , which is arranged to meter the amount of fuel flowing into the following high pressure area of the fuel injection system. From the metering unit 34 the fuel flows into a high-pressure pump 36 , which increases the pressure of the fuel to a high injection pressure of up to several hundred bars. The high-pressure fuel is fed to a high-pressure distributor (common rail) 36 fed. From there, the fuel flows through high-pressure connection lines 40 to directly mounted on the combustion chamber of the internal combustion engine fuel injectors 42 , The fuel injectors 42 be through in the 1 not shown control to inject the fuel as desired in at least one combustion chamber of the internal combustion engine. Excess fuel gets out of the fuel injectors 42 via a return line 44 back to the fuel tank 46 guided.

A fluid injection system according to the in the 1 embodiment shown includes a fluid tank 16 for storing the fluid to be injected into an exhaust line of the internal combustion engine. The fluid tank 16 is via a fluid line 18 and a one-way valve 14 with a fluid pumping device 4 connected. The fluid pumping device 4 is in the embodiment shown as a diaphragm pump with a fuel chamber 8th and a fluid chamber 10 passing through a movable membrane 6 are separated from each other, formed. In the diaphragm pump 4 is also a spring 12 provided on the membrane 6 exerts a force on the membrane 6 pushes into a position in which the volume of the fluid chamber 10 maximum and the volume of the other side of the membrane 6 arranged fuel chamber 8th is minimal. Will the membrane 6 under the action of the force of the spring 12 moves, increases the volume of the fluid chamber 10 and fluid flows out of the fluid tank 16 through the fluid supply line 18 and the one-way valve 14 into the fluid chamber 10 ,

The fuel chamber 8th is via a dosing unit 24 , downstream of the pre-feed pump 30 to the fuel line 29 is connected, hydraulically with the fuel line 29 connected. The dosing unit 24 has a switching valve 26 on, through which the hydraulic connection between the fuel line 29 the fuel injection system and the fuel chamber 8th the diaphragm pump 4 can be produced and interrupted. In addition, the dosing unit 24 a throttle 50 on which the fuel chamber 8th the diaphragm pump 4 hydraulically with the fuel tank 46 combines.

With opened switching valve 26 fuel flows through the pre-feed pump 30 has been brought to an elevated pressure of up to 10 bar, through the switching valve 26 in the fuel chamber 8th the diaphragm pump 4 , This increases the pressure in the fuel chamber 8th the diaphragm pump 4 on and the membrane 6 is against the pressure in the fluid chamber 10 prevails, and the power of the spring 12 down in the direction of the fluid chamber 10 pressed. The one-way valve 14 prevents backflow of the fluid from the fluid chamber 10 into the fluid tank 16 , The fluid flows out of the fluid chamber 10 through the pipe 20 with that of the diaphragm pump 4 generated pressure in the fluid injector 22 , The fluid injector 22 is a pressure wave controlled injector which opens and injects the fluid into an exhaust line (not shown) of the internal combustion engine when the pressure of the fluid in the fluid line 20 reaches a predetermined value.

The injection process is terminated when the membrane 6 at the bottom of the fluid chamber 10 the diaphragm pump 4 strikes or when the switching valve 26 is closed.

With closed switching valve 26 pushes the spring element 12 the membrane 6 upwards in the direction of the fuel chamber 8th , so that the volume of the fluid chamber 10 increases and the volume of the fuel chamber 8th is reduced. Fuel from the fuel chamber 8th flows through the throttle 50 and the drain line 48 back to the fuel tank 46 , Fluid from the fluid tank 16 flows through the fluid supply line 18 and the one-way valve 14 in the enlarged fluid chamber 10 the diaphragm pump 4 and the diaphragm pump 4 is ready for another injection process.

By appropriate activation of the switching valve 26 can the diaphragm pump 4 be operated so that with each delivery stroke the maximum possible pump stroke is utilized. Such a volume control, by the frequency with which the switching valve 26 is controlled, is very accurate, as is the frequency with which the diaphragm pump 4 is controlled, and the maximum pump stroke and thus the maximum flow of the diaphragm pump 4 be set very precisely.

If smaller volume flows are required, the diaphragm pump can 4 be operated with a partial stroke, in which the control valve 26 closed before the membrane 6 reached the lower stop. The flow rate is over the control time of the control valve 26 set. This mode requires a high accuracy of the control valve 26 and the driving time. As the flow rate in this case also from the pressure in the fuel line 29 depends is a pressure sensor 32 in the fuel line 29 helpful to accurately determine the amount of fluid delivered.

2 shows an alternative embodiment of a metering unit according to the invention 24 , The dosing unit 24 instead of in the 1 shown switching valve 26 and the throttle 50 a changeover valve 27 on. Through the switching valve 27 is the fuel chamber 8th the diaphragm pump 4 optionally with the fuel line 29 the fuel injection system or with the fuel return line 48 in the fuel tank 46 leads, connectable.

Is the fuel chamber 8th with the fuel line 29 connected, so fuel flows from the Fuel line 29 in the fuel line 8th , The increased pressure in the fuel chamber 8th moves the membrane 6 down and pushes fluid out of the fluid chamber 10 under increased pressure in the fluid line 20 as related to the 1 described. Because the fluid chamber 8th unlike the one in the 1 embodiment shown not with the fuel tank 46 is connected, a parasitic fuel flow, which in the in the 1 shown embodiment by the throttle 50 and the drain line 48 unused in the fuel tank 46 drains, in which in the 2 shown embodiment avoided. This is the amount of fuel needed to drive the diaphragm pump 4 from the fuel line 29 less than that in the 1 shown embodiment. The front feed pump 30 can therefore be made smaller than in the embodiment shown in the figure.

Upon completion of the fluid injection operation, the switching valve becomes 27 switched so that the fuel chamber 8th via the changeover valve 27 and the drain line 48 with the fuel tank 46 is connected, leaving fuel from the fuel chamber 8th in the fuel tank 46 can drain away. Since no throttle in this embodiment 50 in the hydraulic connection between the fuel chamber 8th and the fuel tank 46 is arranged, the fuel can be particularly fast from the fuel chamber 8th flow away. The membrane 4 therefore moves particularly fast in the upper starting position and the diaphragm pump 4 is particularly fast ready for another injection process. Fluid is therefore injectable at a high frequency in the exhaust system.

3 shows a schematic representation of an alternative embodiment of a diaphragm pump according to the invention 4 ,

Also, this embodiment of a diaphragm pump 4 like the ones in the 1 and 2 embodiments shown a fluid chamber 10 and a fuel chamber 8th on, passing through a movable membrane 6 are separated from each other. The fluid chamber 10 is via a one-way valve 14 and a supply line 18 with a fluid tank 16 and via a drain line 20 with a fluid injector, not shown 22 connected.

Above the fuel chamber 8th and the fluid chamber 10 is a low pressure volume 58 formed with a first cross section Q1. Above the low pressure volume 58 is a high pressure volume 60 formed with a second cross section Q2, wherein the second cross section Q2 is smaller than the first cross section Q1. The low pressure volume 58 is through a piston bore 59 with the fuel chamber 8th connected. Into the piston bore 59 is a lower area 52a a pressure piston 52 so inserted that the lower end of the pressure piston 52 in contact with the membrane 6 stands. An upper, the fuel chamber 8th remote area 52b of the pressure piston 52 has a larger cross section than the lower one 52a Area of the pressure piston. In particular, the cross section of the upper area 52b of the pressure piston is selected so that it is substantially fluid-tight in the cross section Q1 of the low-pressure volume 58 is fitted.

To the lower area 52a of the pressure piston 52 is a spring element 56 , z. B. a coil spring, arranged, each on the lower, the fuel chamber 8th facing the end of the low pressure volume 58 and on the lower end of the low pressure volume 58 facing lower side of the upper area 52b of the pressure piston 52 supported. The pressure piston 52 is so by the spring element 56 elastic in the low pressure volume 58 stored.

About a process 64 is the low pressure volume 58 hydraulically with the fuel tank 46 connected.

Above the low pressure volume 58 is a high pressure volume 60 formed that over an inlet 66 with one of the 1 and 2 known dosing unit 24 hydraulically connected so that pressurized fuel from the fuel line 29 in the 3 Not shown fuel injection system through the metering unit 24 in the high pressure volume 60 is insertable. In the pressure piston 52 is a fuel hole 54 formed the high pressure volume 60 hydraulically with the fuel chamber 8th combines.

With open control valve 26 . 27 in the dosing unit 24 pressurized fuel flows out of the fuel line 29 the fuel injection system through the inlet 66 in the high pressure volume 60 and through the fuel hole 54 in the pressure piston 52 is formed, further into the fuel chamber 8th so that the membrane 6 , as related to the 1 and 2 described, pressed down and the volume of the fluid chamber 10 is reduced.

In addition, the increased pressure in the high pressure volume pushes 60 also the printing cylinder 52 against the force of the spring element 56 down, giving an additional, downward force on the membrane 6 is exercised. This will cause the pressure in the fluid chamber 10 further increases, so that the fluid from the fluid chamber 10 under increased pressure through the drain line 20 in the in the 3 not shown fluid injector 22 flows.

On the lower, the pressure piston 52 opposite side of the membrane 6 is a stroke stop 64 arranged, which the delivery stroke of the membrane 6 limited by being on the bottom of the fluid chamber 10 hits. The stroke stop 64 may be elastic, to the impact of the membrane 6 on the bottom of the fluid chamber 10 To dampen and thereby both the wear and the operation of the diaphragm pump 4 to minimize the development of noise.

Is the membrane 6 firmly with the lower end face of the pressure piston 52 connected, so is an additional spring element 12 in the fluid chamber 10 that the membrane 6 after the completion of the delivery stroke pushes up again, not required because the diaphragm 6 from the pressure piston 52 is pulled up when the pressure piston 52 under the action of the force of the spring element 56 moved back to its upper starting position.

In the in the 3 shown embodiment of a diaphragm pump 4 the injection pressure of the fluid is increased to a pressure which is higher than that of the prefeed pump 30 the pressure generated by the fuel system. Even larger amounts of fluid can be injected into the exhaust system within a very short injection time. The maximum injection quantity per delivery stroke is determined by the dimensioning of the stroke stop 64 adjustable.

Claims (10)

Dosing system for injecting a fluid into an exhaust line of an internal combustion engine, which is connected to a fuel injection system, which is designed to inject fuel under pressure into at least one combustion chamber of the internal combustion engine, wherein the dosing system comprises a pump device ( 4 ) which is designed and hydraulically connected to the fuel injection system such that the fluid can be injected into the exhaust gas line by the pressure generated in the fuel injection system. Dosing system according to claim 1, wherein the pump device ( 4 ) a diaphragm pump with two chambers ( 8th . 10 ), which by a movable membrane ( 6 ) are separated from each other. Dosing system according to claim 2, wherein a first chamber ( 8th ) is hydraulically connected to the fuel injection system and wherein a second chamber ( 10 ) hydraulically with a fluid tank ( 16 ) and a fluid injection member ( 22 ) connected is. Dosing system according to claim 3, wherein the first chamber ( 8th ) via a switching valve ( 26 ; 27 ) is hydraulically connected to the fuel injection system. Dosing system according to one of claims 3 or 4, wherein the fluid injection member ( 22 ) comprises a pressure wave-controlled injector which is attached to the exhaust line and hydraulically connected to the diaphragm pump ( 4 ) connected is. Dosing system according to one of claims 2 to 5, wherein the diaphragm pump ( 4 ) at least one piston ( 52 ) configured to apply a force to the membrane during operation ( 6 ) exercise. Dosing system according to claim 6, wherein the piston ( 52 ) movable between a low-pressure stage ( 58 ) and a hydraulically connected to the fuel injection system high-pressure stage ( 60 ) is arranged so that the piston ( 52 ) is movable by the pressure generated in the fuel injection system. Dosing system according to claim 7, wherein in the piston ( 52 ) a fuel hole ( 54 ) is formed, which the high-pressure stage ( 60 ) hydraulically with the first chamber ( 8th ) connects. Dosing system according to one of claims 2 to 8, wherein in the diaphragm pump ( 4 ) a reset element ( 12 ) is provided which is adapted to an elastic restoring force on the piston ( 52 ) exercise. Dosing system according to one of claims 2 to 9, with at least one stop element ( 64 ), which limits the movement of the membrane ( 6 ) is trained.

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