DE102007030555A1 - Fuel injection pump arrangement for use in commercial vehicle to dispense urea solution for exhaust gas treatment, has common output line in contact with injection valve device such that cylinder capacities are connected to output line - Google Patents

Abstract

The arrangement (1) has cylinders (8, 12) with pistons (7, 11) and two cylinder capacities (8.1, 12.1), where stepping motors (3, 4) are provided for adjusting the pistons. A common output line (24) is in contact with an injection valve device such that the cylinder capacities are connected to the output line. The cylinders are designed such that one of the cylinders is in the working stroke, and the other is provided with a double sided piston pump with two cylinder capacities. Independent claims are also included for the following: (1) a method for injection of a fluid (2) a fuel injection system with a fuel injection pump arrangement.

Description

The The invention relates to an injection pump assembly and a method for injecting a fluid. As a fluid, in particular a urea solution in an exhaust tract of a vehicle to be injected.

to Exhaust gas aftertreatment of vehicles, in particular commercial vehicles, becomes in the selective catalytic reduction (SCR) of nitrogen oxides a urea solution from one carried by the vehicle Urea solution tank taken and injected into the exhaust line in front of the SCR catalyst. Injection is generally by means of a pump and an injector, the z. As the current speed and the current torque of the engine is controlled.

in this connection On the one hand, a precise metering of the injection quantity is required. The one for this used injection pumps are usually relatively large dimensions and expensive. The injection pumps carry the urea solution in Generally an electrically operated injection nozzle to, which takes over the required exact dosage. Thus, a complex one Injection system from injection pump and electrically operated injector required.

Of the Invention is based on the object, an injection pump arrangement and to provide a method of injecting a fluid, the a cost-effective Manufacture and enable safe operation.

These The object is achieved by an injection pump arrangement according to claim 1 and a method according to claim 9 solved. Describe the dependent claims preferred developments.

Of the Invention is based on the idea, by a piston pump system with two or more displacements a certain injection pressure on an output line available put.

in this connection can according to a first embodiment the injection pressure constantly or continuously available be put, z. B. by staggered, partially overlapping strokes of two displacements two piston pumps. In such a system is thus the interposition a pressure accumulator basically not required, so with small dimensions nevertheless a high pressure or a high injection dynamics is achieved. in this connection can the two piston pumps in particular also clock-offset or be operated in the process cycle offset that their the injection pressure supplying working strokes overlap in the beginning and / or end phases, so that at least continuously a piston pump or a cylinder is in the working stroke.

at overlapping Initial and / or final phases thus becomes the power of an engine just before his dead center slowly shut down to zero and the As a result, required residual power due to the approaching taken over another pump. As a result, the occurrence of non-pressurized dead phases can be avoided become.

According to the invention of return stroke especially with a higher one Piston speed, d. H. a higher motor frequency than the Working stroke performed so that at the end of the working stroke still sufficient reserve for the continuous takeover the lifting work for the takeover by the other cylinder remains.

Also according to the invention the back of the Cylinder, d. H. the back Piston space to be filled with the working fluid or the fluid. This will create a dynamic seal with corresponding leaks and thereby avoiding crystallization of urea avoided. The back piston chamber so sucks while the working stroke, the fluid and there are during the Rückstellhubes depressurized or only with the pressure specified by the tank.

Instead of of two engines can z. B. also a common motor to the drive the at least two cylinders may be provided, these correspondingly having a Gear device are suitably coupled together, so that always a corresponding flow rate, preferably a uniform flow rate, is issued. The delivery rate itself can over here the engine speed can be adjusted.

at Use of more than two piston pumps or cylinder-piston units can the strokes each offset to each other, so that between two cylinders occurring transition phases each covered by the third motor; thus are at such training no gradual in speed varied transitions required.

In a second embodiment, according to the invention, a double-sided piston pump can be used, in which the two sides of an adjusted piston in each case a displacement is formed and cause both displacements alternately in working strokes, the promotion of urea solution. Thus, a small-sized very cost-effective solution can be achieved with only one cylinder. In this case, although a brief drop in the delivery pressure occurs in the respective mechanical reversal points. This may optionally erfindungsge However, be achieved by overcompensation by brief pressure increase before the mechanical reversal point, and / or by a pressure storage in the output line as a low-pass. In this case, the low-pass behavior of the outlet line system, or the catalyst, may already be sufficient, or a small pressure accumulator may be installed, if necessary. In such a system, an automatic venting at first commissioning by eteratives increase the adjustment carried out under measurement of the output pressure.

at both embodiment can the one or more piston pumps, in particular via an electric motor device and one or two spindle gears are driven. This can in particular One or two stepper motors are used, each one Drive the piston pump so that it is suitable for the respective operating situation the injection engine required injection pressure provided becomes.

at Using stepper motors will sense the adjustment stroke allows by the non-energized windings of the respective stepping motor the actual Sensation of the step.

Farther can in the two-cylinder embodiment When using stepper motors, the motor during Rückstellhub go against a mechanical stop, whereupon he subsequently in a shorter time Time interval remaining steps without a mechanical adjustment executing, before it is switched to the working stroke.

A corresponding Ventilbeschaltung can according to the invention the fluid flow make sure, with z. B. tank connections of the displacement via check valves connected to the tank, so that they during the working of the respective displacement can not return the fluid to the tank. at the two-cylinder embodiment the connection is made to the back Piston chambers without such valves. Furthermore, working outputs of the displacements are advantageously above each a check valve connected to the common output line, allowing pressurization the output line without a return of the Fluids from the cylinder in the working stroke to the other Cylinder possible is.

The injection pump assembly according to the invention allows in particular, the use of an injector without electrical actuation. This can be both a direct mechanical injection and an atomizer nozzle with additional Compressed air supply can be realized, this z. B. by check valves and nozzles or chokes can be formed. When injecting into one Venturi nozzle or similar Pressure reduction device can be the air pressure against which the fluid is to be injected, kept low.

The Invention will be described below with reference to the accompanying drawings on some embodiments explained. Show it:

1 an injection pump assembly according to an embodiment of the invention;

2 a time diagram of the frequencies and speeds of the in 1 used engines;

3 an inventive urea injection system with the injection pump arrangement 1 without air atomization;

4 an inventive urea injection system with the injection pump arrangement 1 and with air atomization;

5 an injection pump assembly with double-sided piston pump;

6 an inventive urea injection system with the injection pump arrangement 5 without air support;

7 an inventive urea injection system with the injection pump arrangement 5 and with air atomization according to an embodiment;

8th an inventive urea injection system with the injection pump arrangement 5 and with air atomization according to another embodiment;

9 a time chart of the setpoint and the actual value of the delivery volume of the second embodiment as a function of time.

An injection pump arrangement 1 has a designed as a control electronics control device 2 , a first stepper motor 3 and a second stepper motor 4 on, by the control device 2 be controlled. The first stepper motor 3 drives via a spindle drive 5 a piston rod 6 a first piston 7 on, in a first cylinder 8th slidably guided. The first piston 7 divides the cylinder interior of the first cylinder 8th thus in an in 1 to the left of the first piston 7 lying displacement 8.1 and a piston chamber to the right 8.2 ,

The second stepper motor drives accordingly 4 via a second spindle gear 9 a second piston rod 10 a second piston 11 on, the interior of a second cylinder 12 in a cubic capacity 12.1 and a back piston chamber 12.2 divided. The stepper motors 3 and 4 can in particular be connected in unipolar operation in each case such that their non-energized windings sense the actually performed step.

The two cylinders 8th and 12 each have three fluid connections, namely a tank connection 8.3 respectively. 12.3 of the displacement 8.1 respectively. 12.1 , a tank connection 8.4 respectively. 12.4 of the piston chamber 8.2 respectively. 12.2 and one to the respective displacement 8.1 respectively. 12.1 connected output terminal 8.5 respectively. 12.5 on.

The displacement 8.1 and 12.1 are about their tank connections 8.3 and 12.3 each via a check valve 14 respectively. 15 to a tank line 25 connected, such as. In 3 . 4 shown to a tank 16 with a urea solution, so that the displacement 8.1 and 12.1 the liquid only from the tank 16 suck in, but not in the tank when pumping 16 can press back. The functionally not relevant piston chambers 8.2 and 12.2 at the back of the pistons 7 and 11 are directly to the tank 16 connected so that they are each filled with urea solution and thus both sides of the piston 7 and 11 always in contact with urea solution and not with air. The piston rods 6 and 10 are each about a bellows 18 respectively. 19 sealed, so that no more dynamic sealing point is present at which the urea solution can come into contact with air.

The output connections 8.5 and 12.5 each have a check valve 20 and 21 to a common output line 24 connected, with the check valves 20 and 21 prevent the respectively promoting cylinder 8th or 12 Liquid in the displacement of the other cylinder 12 respectively. 8th suppressed. Advantageously, a pressure sensor 26 to the output line 24 connected and outputs a measurement signal to the controller 2 out. To the output line 24 are one or more injector devices 28 . 30 connected below with respect to 3 . 4 be described in more detail.

According to the invention, the two stepper motors 3 and 4 controlled such that the sum of the flow rate of both cylinders 8th and 12 always the desired total amount, so here the injector devices 28 . 30 provided injection quantity corresponds. For this purpose, the cylinders 8th and 12 about their engines 3 respectively. 4 clocked offset, as in the time chart of 2 is explained in more detail.

2 shows as a function of time t from top to bottom, the frequency f1 of the first stepping motor 3 , the speed v1 of the first stepping motor 3 , the frequency f2 of the second stepper motor 4 and the speed v2 of the second stepper motor 4 ,

According to 2 the first cylinder drives 8th from time t1 to time t2 clockwise, ie according to 1 in the return stroke RH1 serving as the intake stroke while reducing its rear-side piston space 8.2 and increasing its capacity 8.1 until the first piston 7 at time t2 against a right stop moves and from the non-energized windings of the first stepping motor 3 no signal comes. Until the time t3, a few reserve steps of the first engine still take place 3 until it is switched to counterclockwise rotation, ie the working stroke AH1, in t3. In this case, the frequency f1 and thus the speed v1 is gradually increased from t3 to t4. During the counterclockwise rotation, the steps actually taken are sensed. After a certain number of steps, at time t6, the frequency f1 of the first stepping motor becomes 3 slowly shuts down to zero and reaches standstill at time t7, while the frequency f2 of the second stepper motor 4 from t6 to t7 is slowly increased from zero. In this phase between t6 and t7 and accordingly in the overlap phase between t3 and t4, thus sharing the two engines 3 and 4 the work. Instead of a linear increase and decrease of the frequencies 1 . 2 and velocities v1, v2, other transitions are possible; only the total volume change is relevant, ie the sum of the speeds.

After the second stepper motor 4 in t7 - corresponding to the previous cycle at t1 - has taken over all the work, drives the first stepper motor 3 back in the next return stroke RH1 to the right stop. This is done with a slightly higher first frequency f1 and thus the amount of higher first speed v1 than during the working stroke AH1. This will save the time for gradually taking over the lifting work and for the reserve steps. By no pumping power is required during the clockwise rotation, ie intake stroke or return stroke RH1 and RH2, the first stepping motor 3 and accordingly also the second stepper motor 4 each be driven at a higher frequency f1 or f2, without the risk that the respective engine 3 respectively. 4 stop.

At the end of the working stroke of the respective cylinder 8th respectively. 12 According to the invention, there is still sufficient reserve for the mechanical stop, so that the continuous takeover of the lifting work of the respective other cylinder 12 respectively. 8th not disturbed.

In the return strokes RH1 and RH2 serving as suction strokes, that is, in the illustrated embodiment of the right-turn driving, no slow increase of the speed is required. The provision is thus made quickly and at high speed, so that more time is available for the working strokes and the overlap according to the invention of the operation of both stepper motors 3 and 4 in the work strokes AH1 and AH2 between t3 and t4 and between t6 and t7.

3 shows an application in a urea injection system for exhaust aftertreatment. To the output line, which is constantly under pressure during operation 24 is an injection nozzle device 28 or injection nozzle connected, which does not require an electric drive for generating the injection jet and advantageously also no electrical control. The injector 28 has for this purpose a check valve R1 and an output nozzle 29 on.

4 shows an application in a urea injection system with air atomization. The compressed air injection nozzle 30 has check valves R1, R2 and R3 and a throttle (nozzle) D1 and a dispensing nozzle 31 on and off with its fluid connection 32 to the output line 24 as well as with their compressed air connection 33 connected to a compressed air line. By injecting the additional compressed air into the compressed air injection nozzle 30 the atomization quality is increased. Another function is to blow out the output line 24 at low outside temperatures to prevent the urea solution from freezing.

The pressurized urea solution becomes the dispensing nozzle via the check valve R1 31 directed. The check valve R1 is here biased by a spring to prevent dripping of the liquid.

The check valve R2 prevents the penetration of urea into the compressed air system.

For blowing out the output line 24 is the electrically operated 2/2-way valve (solenoid valve) M1, which in this embodiment between the tank 16 and the output line 24 is switched on, opened. The amount of compressed air is increased beyond what is necessary for sputtering, so that the back pressure from the nozzle D1 becomes so great that the check valve R3 opens. This allows the compressed air, the urea solution via the solenoid valve M1 back into the tank 16 promote.

An essential advantage of the embodiment of 4 is because there are no electrical components in the compressed air injection nozzle exposed to the heat of the catalyst 30 are provided.

Instead of the stepper motors 3 . 4 Other types of engines can be used. Furthermore, a common motor or a common motor-gear unit, for. B. with different gear stages for controlling the two piston rods 6 and 10 be used.

Especially with bipolar stepper motor control, an additional Sensor winding integrated in the stepper motor, which is the number the actual completed steps sensed.

In the 5 to 9 an injection pump assembly according to another embodiment of the invention is shown in which instead of two cylinder-piston units, a double-sided piston pump 40 is provided, which is a cylinder 41 , one in the cylinder 41 guided piston 42 and a piston rod 43 having. The piston 42 divides the cylinder interior into a first, front displacement 44 and a second, rear displacement 45 , The two displacements 44 . 45 each have a work connection 44a . 45a and a fluid outlet 44b . 45b on. The work connections 44a . 45a are each via a designed as a check valve inlet valve 46 . 47 to one of a tank 16 with urea solution leading tank line 25 connected. The fluid outlets 44b . 45b are each about an outlet valve designed as a check valve 48 respectively. 49 to the common output line 24 connected, the lines 25 . 24 in their function those of the first embodiment of the 1 to 4 correspond. The valves 44a . 45a . 44b . 45b thus allow the connection to the common lines 24 and 25 while avoiding a hydraulic short circuit. Thus, the respective pressure side of the cylinder 41 via a check valve with the output line 24 and the respective suction side via a check valve with the tank line 25 connected.

The piston rod 43 in turn is powered by a stepper motor 50 via a gearbox 51 driven, the stepper motor 50 again from an electronic control device 2 is controlled, which is either an output signal of the stepping motor 50 can record as input, z. As a signal induced in a non-energized motor winding signal, and / or via a pressure sensor 26 the outlet pressure in the outlet line 24 measures.

The stepper motor 50 adjusts the piston 42 in a periodic stroke movement within the cylinder 41 , wherein the piston pump 40 in each stroke - to the left or to the front and to the right or to the rear - from the decreasing displacement 44 or 45 Urea solution in the outlet line 24 pumps and with each because magnifying capacity 45 or 44 at the same time urea solution from the tank line 25 receives.

Also in this embodiment, the crystallization of leaking in the piston rod guide urea solution can be safely prevented by supplementary measures. First of all is in the cylinder 41 a piston rod seal 54 intended. Furthermore, between the back of the cylinder 41 and the piston rod 43 a bellows 55 attached. The bellows interior 56 may advantageously also with urea solution from the tank 16 be filled. This is how in 5 . 6 shown to the tank line 26 , or alternatively directly to the tank 16 , a supply line 57 connected directly to the bellows 55 or - as in 5 . 6 shown - over in the back area of the cylinder 41 trained execution 58 so that the bellows 55 no connection for the supply line 57 having. By connecting the bellows interior 56 to the urea line system is the bellows interior 56 thus always periodically filled and emptied with urea solution in the piston adjustments. Because the piston rod 43 on both sides of its passage through the cylinder 41 is permanently surrounded by urea solution, no crystallization of urea solution occurs in air. In 5 is the connection of the supply line 57 to the tank line 25 shown; Alternatively, the connection of the supply line 57 but also directly to the tank 16 respectively. The embodiment shown with the connection to the tank line 25 is usually a smaller length of the feed line 57 require. A connection to the tank 16 , in particular to the tank upper edge or an upper region of the tank 16 , may be particularly useful if the level of the piston pump 40 and thus also the bellows 55 under the tank 16 because then it can be prevented that in case of a defect of the bellows 55 the entire tank 16 expires.

Basically, the connection of the bellows 55 However, be omitted to the urea solution system.

According to 6 is the output line 24 directly to an injection nozzle device 28 connected with a nozzle valve 29 the urea solution directly into a catalyst 59 (SCR catalyst) injected.

According to the embodiment of the 7 the urea solution is out of the outlet line 24 over a nozzle 60 first into a compressed air system of a compressed air connection (compressed air line) 33 against the air pressure of z. B. 5 bar injected and the aerosol thus formed via an injection nozzle 62 in the catalyst 59 injected.

8th shows a modified embodiment, in which the injection nozzle 60 the urea solution from the outlet line 24 in a relaxed air behind a Venturi nozzle 64 injects. The in the compressed air connection (compressed air line) 33 present air pressure of 5 bar is in the venturi 64 reduced to 1 bar, so that the injector or the piston pump 40 not working against full air pressure, but only against about 1 bar. The aerosol is in turn via an injection nozzle 62 in the SCR catalyst 59 injected.

In the 4 . 7 and 8th An aerosol is formed and in a mixing tube 64 to the respective injection nozzle 29 respectively. 62 promoted. The injection systems on the one hand the 3 and 6 and on the other hand the 4 . 7 and 8th Although here are each shown only in one embodiment, but they can optionally also in both embodiments of 1 or 5 be used.

When commissioning for the first time, the system or the injection pump arrangement must first be filled with urea solution, ie vented. This is the stepper motor 50 from the controller 2 switched on and starts in any direction. Thus, by one of the two displacements 44 or 45 in the output line 24 a dynamic pressure in front of the injection nozzle 31 respectively. 60 built up. Instead of the injector used for continuous operation 31 respectively. 60 can also be used according to the invention, a special commissioning, so that no urea solution enters the cold exhaust tract. The pressure generated is from the pressure sensor 26 or another pressure sensor sensed. When the piston 42 reaches its mechanical stop in the set direction, registered the sensor 26 a pressure drop. The stepper motor 50 then moves in the opposite direction. He gets so many steps that he reverses shortly before the other mechanical stop. The stepper motor 50 Now always moves with a certain reserve between the two mechanical stops back and forth until the entire system is completely filled with urea solution. This is preferably done with a high step frequency. At the end of this initial operation, the last direction of rotation and the number of steps traveled is after the last reversal point in the control device 2 stored so that the direction of rotation and the number of steps between the mechanical stops are now known and stored.

At the respective start of operation, ie after starting the internal combustion engine, the stepping motor 50 each operated in the same direction as before the last time parking or after the initial operation. Depending on the required injection quantity, the stepper motor 50 with a certain frequency applied. By storing the previously completed steps after the last reversal point, it is now possible to use the stepper motor 50 just drive until just before the next reversal point.

The pressure sensor 26 measures the dynamic pressure in the outlet pipe 26 , As a result, it can be recognized that the stepper motor 50 with the piston adjusted by him 42 moves against an end stop if steps have been lost during operation or have not been set effectively. The working stroke can then be symmetrized again accordingly. Furthermore, blockages of the nozzle can be detected. In this case, the stepper motor 50 operated at a lower frequency ben, so that a higher power output is possible and the nozzle 31 respectively. 62 can be freely pressed thereby. These measures are basically also in the first embodiment of 1 to 5 possible.

The injection pump arrangement can in principle also without pressure sensor 26 be operated by the number of steps actually performed - as in the first embodiment - is sensed. For this purpose, a sensor winding in the stepper motor 50 be provided, or turn, the respective non-energized motor winding act as a sensor winding.

In the second embodiment falls at the reversal point of the piston pump 40 the promotion always for a short time, since there are no overlap periods of the working strokes two displacements, as shown in the first embodiment. However, the pressure drop can be compensated according to the invention. On the one hand, it can be used to control the stepper motor 50 by the control device 2 be taken into account. 9a shows the nominal value SV of the delivery volume (volume per unit time), 9b the corresponding actual value IV. The setpoint SV first increases from a time t11 to a time t12 and remains constant from then until beyond the next reversal point t14. This ideal setpoint can be set according to 9b be approximated in which the software of the controller 2 this is taken into account and the stepper motor 50 Thus, at a time t13 is controlled such that it injects more. The increased injection quantity between t13 and t14 corresponds essentially to the drop between the reversal point t14 and the time t15, in which the ideal delivery volume is reached again in the return stroke.

The injection quantity additionally injected between t13 and t14 can be connected to the output line 24 connected elastic hydraulic accumulator, or even temporarily stored in the catalyst itself. Such a low-pass behavior or intermediate storage can in general already be directly attributed to the elasticity of the output line system 24 be reached, and optionally also in the filled with the aerosol compressed air supply line in front of the injection nozzle.

Because the right displacement 45 due to the running through him Kobenstange 43 has a slightly smaller diameter than the left displacement 22 , the piston can pump 40 to be driven faster during the return, with correspondingly less force is required.

Claims (40)

Injection pump arrangement for dispensing a fluid, in particular a urea solution for exhaust aftertreatment, wherein the injection pump arrangement ( 1 ) at least comprising: a cylinder device ( 8th . 12 . 41 ) with at least one piston ( 7 . 11 . 42 ) and at least two displacements ( 8.1 . 12.1 . 44 . 45 ), a motor device ( 3 . 4 . 50 ) for adjusting the at least one piston ( 7 . 11 . 42 ), and a common output line ( 24 ) for connecting an injection nozzle device ( 28 . 30 ), wherein the at least two displacements ( 8.1 . 12.1 . 44 . 45 ) to the common output line ( 24 ) are connected. Injection pump arrangement according to claim 1, characterized in that the displacement ( 8.1 . 12.1 . 44 . 45 ) of the at least one cylinder ( 8th . 21 . 41 ) one tank connection ( 8.3 . 12.3 . 44a . 45a ), each via a check valve ( 14 . 15 . 46 . 47 ) to a tank line ( 25 ) for connection to a fluid tank ( 16 ) connected. Injection pump arrangement according to claim 1 or 2, characterized in that working connections ( 8.5 . 12.5 . 44b . 45b ) of the cubic capacity ( 8.1 . 12.1 . 44 . 45 ) via a respective check valve ( 20 . 21 . 48 . 49 ) to the common output line ( 24 ) are connected. Injection pump arrangement according to one of the preceding claims, characterized in that the cylinder device comprises at least: a first cylinder ( 8th ) with a first piston ( 7 ), and a first displacement ( 8.1 ), a second cylinder ( 12 ) with a second piston ( 11 ) and a second displacement ( 12.1 ), the engine device ( 3 . 4 ) for clock-offset adjustment of the two pistons ( 7 . 11 ) is provided, and always at least one cylinder ( 8th . 12 ) is in the working stroke. Injection pump assembly according to claim 4, characterized in that the two pistons ( 7 . 11 ) are clock-shifted in such a way that they are in opposite directions for a predominant part of the clock cycle (t1-t6) and overlap in the beginning and / or end phases (t3-t4; t6-t7) of their working strokes (AH1, AH2). Injection pump assembly according to claim 5, characterized characterized in that the working strokes (AH1, AH2) are located both in overlap in their final phases as well as in their initial phases. Injection pump arrangement according to one of claims 4 to 6, characterized in that the motor device comprises two stepper motors ( 3 . 4 ), each having a piston ( 7 . 11 ) adjust. Injection pump arrangement according to one of claims 4 to 7, characterized in that behind the piston ( 7 . 11 ) formed piston chambers ( 8.2 . 12.2 ) filled with fluid and with a tank connection ( 25 ) are connected. Injection pump arrangement according to one of claims 4 to 8, characterized in that piston rods ( 6 . 10 ) The piston ( 7 . 10 ) via flexible seals fixedly attached to them ( 18 . 19 ), z. B. bellows are sealed. Injection pump arrangement according to one of claims 1 to 3, characterized in that the cylinder device ( 41 ) a cylinder ( 41 ) with a double-sided piston ( 42 ), the cylinder interior in a first displacement ( 44 ) and second displacement ( 45 ), where both displacements ( 44 . 45 ) each have a working connection ( 44a . 45a ) and a fluid outlet ( 44b . 45b ), and wherein the displacement ( 44 ) 45 ) are alternating in a power stroke and intake stroke. Injection pump arrangement according to claim 10, characterized in that the working connections ( 44a . 45a ) of the two displacements ( 44 ) 45 ) to a common tank line ( 25 ) and the fluid outlets ( 44b . 45b ) of the two displacements ( 44 ) 45 ) to a common output line ( 24 ) are connected. Injection pump arrangement according to claim 10 or 11, characterized in that between the cylinder ( 41 ) and a piston rod ( 43 ) of the piston ( 42 ) a flexible connection, for. B. a bellows ( 55 ), whose interior ( 56 ) is filled with the fluid. Injection pump assembly according to claim 12, characterized in that an Innraum ( 56 ) of the flexible connection ( 55 ) to a fluid tank ( 16 ) connected. Injection pump arrangement according to claim 13, characterized in that in the cylinder ( 41 ) an implementation ( 58 ) is formed, which the interior ( 56 ) of the connected flexible connection (55) with a fluid line ( 57 ) to the fluid tank ( 16 ) connects. Method for injecting a fluid, in which a fluid in each case in intake strokes in a first displacement ( 8.1 . 44 ) and a second displacement ( 12.1 . 45 ) a piston pump device ( 8th . 12 . 40 ) and in working strokes (AH1, AH2) to a common output line ( 24 ) for transfer to an injection nozzle device ( 28 . 30 ). Method according to claim 15, characterized in that a first cylinder ( 8th ) with a first piston ( 7 ) and the first displacement ( 8.1 ) as the first piston pump and a second cylinder ( 12 ) with a second piston ( 11 ) and the second displacement ( 12.1 ) is operated as a second piston pump, wherein the two cylinders ( 8th . 12 ) in their working strokes (AH1, AH2) a recorded fluid from their displacements ( 8.1 . 12.1 ) to a common output line ( 24 ) for transfer to a Einspritzdüseneinrich device ( 28 . 30 ) and in their return strokes (RH1, RH2) the fluid in each case in their displacements ( 8.1 . 12.1 ), whereby the working strokes (AH1, AH2) and return strokes (RH1, RH2) of the two cylinders ( 8th . 12 ) are offset from each other and where always at least one cylinder ( 8th . 12 ) is operated in the working stroke. Method according to claim 16, characterized in that the process cycles (t1-t7) of the two cylinders ( 8th . 12 ) are offset in such a way that the pistons ( 7 . 11 ) a predominant part of the process cycle are performed in opposite directions and overlap in the beginning and / or end phases (t3-t4; t6-t7) of their working strokes (AH1, AH2). A method according to claim 17, characterized in that the working strokes (AH1, AH2) of the two cylinders ( 8th . 12 ) overlap each in the final phase and initial phase of each working stroke. Method according to claim 17 or 18, characterized in that the pistons ( 7 . 11 ) are respectively accelerated or decelerated in the final phases and / or initial phases of the working stroke. Method according to claim 19, characterized in that the pistons ( 7 . 11 ) are linearly adjusted from a standstill to a subsequently substantially constant Arbeitshubgeschwindigkeit or Rückstellhubgeschwindigkeit in the initial phases and / or end phases of the strokes. Method according to claim 19 or 20, characterized in that the two cylinders ( 8th . 12 ) together provide substantially the same initial pressure (p) throughout the process cycle. Method according to one of claims 16 to 21, characterized in that the pistons ( 7 . 11 ) are adjusted during the working stroke with a lower adjustment than during the return stroke. Method according to claim 22, characterized in that that the return strokes (RH1, RH2) over a shorter one Time duration as the working strokes (AH1, AH2). Method according to one of claims 16 to 23, characterized in that in rear piston chambers ( 8.2 . 12.2 ) the cylinder ( 8th . 12 ) behind the pistons ( 7 . 11 sucked the fluid during the working strokes and during the return strokes to a tank line ( 25 ) is output. Method according to one of claims 15 to 23, characterized in that the pistons ( 7 . 11 ) via a stepping motor device ( 3 . 4 ) with one or two stepper motors ( 3 . 4 ) are adjusted. Method according to claim 25, characterized in that the motors ( 3 . 4 ) travel towards a mechanical stop at the end (t3, t5) of its return stroke (R1, R2) and make some reserve steps in a subsequent time interval (t2, t3, t5, t6). Method according to claim 25 or 26, characterized that the actual completed steps are sensed at least the working stroke, z. B. over non-energized windings of the stepper motor device or via additional sensor windings. A method according to claim 15, characterized in that a double-sided piston pump ( 40 ) is used with one in a common cylinder ( 41 ) guided piston ( 42 ), the cylinder interior in the first and second displacement ( 44 . 45 ), which are alternately reciprocally in suction strokes and working strokes and the fluid from a common tank line ( 25 ) to a common output line ( 24 ). A method according to claim 28, characterized in that the fluid further from the tank line ( 25 ) an interior ( 56 ) connected to the cylinder and a piston rod flexible connection ( 55 ) is supplied. A method according to claim 28 or 29, characterized in that during a first start-up for venting the injection pump arrangement, a motor device, preferably a stepper motor ( 50 ), the piston ( 42 ), whereupon a sensed pressure drop as a mechanical stop of the piston ( 42 ), then the motor device moves in the opposite direction and reversed again just before the other mechanical stop, whereupon the engine device ( 50 ) now always with a certain reserve between the two mechanical stops back and forth until the entire system is completely filled with urea solution. A method according to claim 30, characterized in that after the first operation, the last direction of rotation and the number of steps covered are stored after the last reversal point, so that the direction of rotation and the number of steps between the mechanical stops are now known and stored, wherein at the respective start of operation, preferably after starting a vehicle engine, the engine equipment ( 50 ) operated respectively in the same direction as before the last time parking or after the initial process. Method according to one of claims 15 to 31, characterized in that the output to the output line pressure (p) measured and the measurement signal for adjusting the cylinder ( 8th . 12 ) is used. Method according to one of claims 15 to 22, characterized in that the of the cylinders ( 8th . 12 ) to the common output line ( 24 ) discharged fluid in a subsequently operated without electrical connection injection nozzle device ( 28 . 30 ) is received and injected into an exhaust tract. A method according to claim 33, characterized in that the fluid of the injection nozzle device ( 30 ) is atomized and discharged by means of compressed air. A method according to claim 33, characterized in that the fluid in a region of relaxed compressed air, for. B. behind a Venturi nozzle ( 64 ) is supplied. Injection system with an injection pump arrangement according to one of claims 1 to 14 and one to the common output line ( 24 ) connected injector ( 29 . 30 ), which is free of electrical operation. Injection system according to claim 36, characterized in that the injection nozzle device ( 28 . 30 ) a check valve (r1) and an outlet nozzle ( 29 . 31 ) for the delivery of the fluid in one Has exhaust gas station. Injection system according to claim 37, characterized in that the injection nozzle ( 30 ) a compressed air connection ( 33 ) and a formed from the fluid and supplied compressed air aerosol an injection nozzle ( 31 . 62 ) is supplied. Injection system according to claim 38, characterized in that the compressed air connection ( 33 ) is connected via a second check valve (r2) and a throttle or nozzle (D1) to an output side of the first check valve (R1) and via a further check valve (R3) to an input side of the first check valve (R1). Injection system according to claim 38, characterized in that a nozzle ( 64 ) for relaxing the compressed air, preferably a Venturi nozzle ( 64 ), to the compressed air connection ( 33 ) and an injection nozzle ( 60 ) is provided for injecting the fluid in the relaxed compressed air.