WO2008077408A1

WO2008077408A1 - Pump for feeding urea to an engine exhaust system

Info

Publication number: WO2008077408A1
Application number: PCT/DK2007/050077
Authority: WO
Inventors: Niels Torp Madsen; Christian Boe; Hans Henrik Jochumsen
Original assignee: Grundfos Nonox AS
Current assignee: Emitec Denmark AS
Priority date: 2006-12-22
Filing date: 2007-06-27
Publication date: 2008-07-03
Anticipated expiration: 2009-06-22

Abstract

Pump for measuring out and feeding liquefied urea to a nozzle arranged in an exhaust system of an engine. The pump comprising: a first and a second void (13, 24), the volumes of the voids are de-/increasable thereby each having a displacement volume and being in fluid communication with each other via a one way valve connection valve (7) allowing fluid to flow from the first void and to the second void only, the first void comprising an inlet for receiving fluid from a fluid source and the second void comprising an outlet for delivery of fluid; a one way inlet valve (6) connected to the first void (13) and allowing fluid to flow into the first void only; and an actuating device adapted to de- and increasing the volumes of the voids so as to provide as pumping of fluid through the pump.

Description

PUMP FOR FEEDING UREA TO AN ENGINE EXHAUST SYSTEM

The present invention relates to a pump and a method for operating the pump. The invention relates in particular to a double action pump designed to measuring out and pressurising liquid to a relatively high pressure, such as 4-400bar. A particularly preferred embodiment relates to measuring out and feeding liquefied urea to a nozzle arranged in an exhaust system of an engine.

INTRODUCTION TO THE INVENTION

Administration of a liquid has been found to be a delicate matter especially when the liquid to be administrated is to be administrated in the form of droplet formed by an atomization process performed by a nozzle and when the amounts of liquid to be administered varies over at least one to two decades.

In connection with the present invention, which in particular preferred embodiments, deals with administration of liquefied urea in the form of droplets into an exhaust system, it has been found that the amounts needed to be introduced varies at least two decades, e.g. the amounts to be administered varies from 0.2 l/h to 7.5 l/h.

Furthermore, the pressure at which the liquid is delivered to the atomization parts of the nozzle must be sufficiently high to assure that the fluid actually is atomised and not, as some time is the result when the pressure level is to low, flows creepingly out of the nozzle without any atomization taking place.

BRIEF DESCRIPTION OF THE INVENTION

In a first aspect the present invention relates to a pump comprising a first and a second void, the volumes of the voids are de-/increasable thereby each having a displacement volume and being in fluid communication with each other via a one way valve connection valve allowing fluid to flow from the first void and to the second void only, the first void comprising an inlet for receiving fluid from a fluid source and the second void comprising an outlet for delivery of fluid, a one way inlet valve (6) connected to the first void (13) and allowing fluid to flow into the first void only, an actuating device adapted to de- and increasing the volumes of the voids so as to provide as pumping of fluid through the pump.

In the present context a number of technical terms are used and these should normally be interpreted in way common to a person skilled in the art. For instance: "Displacement volume" typically means the volume change in a cylinder when a membrane, piston or the like is displaced in the cylinder.

"Cylinder" is typically used to denote a void in which a piston is arranged, in which a flexible membrane constituting one ore more sides or the like. Although, a cylinder in many of the embodiments shown herein is cylindrical, this needs not always to be the case. For instance, the cylinder may have a square cross section.

"Pumping cycle". A pumping action is typically a recurring action and may include a period where no fluid is pumped out of the pump. A pumping cycle typically means such a recurring action and is normally considered to begin when fluid starts to be pumped out of the pump and ending just before the pattern is repeated.

In a second aspect, the invention relates to a system for administrating fluid, preferably liquefied urea, into an exhaust system of a vehicle, the system comprising a pump as described above, a fluid reservoir connected to the inlet of the pump and a nozzle connected to the outlet of the pump, wherein the nozzle is arranged in the exhaust system so as to atomize and spray the thereby formed droplets into the exhaust system.

In a further aspect, the invention relates to a method of measuring out liquefied urea, the method comprising using a pump or a system according to the first or second aspect of the invention. The pump is preferably at its inlet connected to a reservoir of liquefied urea and at its outlet connected to a nozzle.

The invention, and in particular preferred embodiments thereof will be disclosed in further details below in connection with the accompanying drawings in which:

Fig. 1 shows schematically a first embodiment of a double action piston pump according to the present invention; fig. Ia shows a first state of the pump and fig. Ib shows a second state of the pump,

Fig. 2 shows schematically a principle of a membrane pump according to the present invention; fig. 2a shows the mechanical parts of the pump and fig. 2b shows the outlet flow profile,

Fig. 3 shows schematically a membrane pump according to the present invention; fig. 3a shows the mechanical parts of the pump and fig. 3b shows the outlet flow profile, Fig. 4 shows schematically a membrane pump according to the present invention; fig. 4a shows the mechanical parts of the pump and fig. 4b shows the outlet flow profile,

Fig. 5 shows schematically a piston pump according to the present invention; fig. 5a shows the mechanical parts of the pump and fig. 5b shows the outlet flow profile,

Fig. 6 shows schematically a piston pump according to the present invention; fig. 6a shows the mechanical parts of the pump and fig. 6b shows the outlet flow profile,

Fig. 7 shows schematically one possible application of the invention, wherein it is used for pumping fluid to a nozzle for atomization of urea and spraying the thereby generated droplet into an exhaust gas of a combustion engine or gas turbine,

Fig. 8 shows schematically a pump with a corbi-stepped piston according to preferred embodiments of the present invention,

Fig. 9 and 10 each shows schematically a cross sectional view of a pump according to preferred embodiments of the present invention,

Fig. 1 shows schematically a double action pump 1. The pump 1 comprises a cylinder 2 and a piston 3 moveable in opposite directions within the cylinder 2 by the rod 4. The displacement volumes of the piston pump are indicated by reference signs A and B in fig. 1. An inlet channel 5 with a one way inlet valve 6 is connected to the cylinder 2. A connection channel 8 with a one way connection valve 7 connects the two ends of the cylinder 1 as shown in fig. 1. Further, an outlet channel 9 is connected at the end of the cylinder 1 as shown in fig. 1.

The pumping action of the pump 1 is performed by displacing the piston 3 by pulling and pushing the piston 3 by use of the rod 4. When the piston 3 moves to the right, with reference to fig. Ia, the volume A increases resulting in closing of the connection valve 7 and opening of the inlet valve 6 whereby fluid is drawn from the reservoir 10 into the volume A via the inlet valve 6. Thus, by moving the piston 3 so as to increase the volume A this volume will be filled with fluid from the reservoir 5. At the same time, the volume B will decrease and as the connection valve 7 is closed so that fluid can not flow to volume A from volume B, fluid present in volume B will be forced out of the cylinder 2 through the outlet channel 9.

When the piston 3 moves to the left, with reference to fig. Ib, volume B increases and volume A decreases. The decrease of the volume A results in opening of connection valve 7 and closing of the inlet valve 6 thereby forcing fluid present in volume A to flow via the connection channel 8 into volume B.

The flows involved are (equation 1):

Inlet flow: V_A=Area of piston*Displacement of piston Outlet flow: V_B=Area of piston*Displacement of piston

when the piston moves to the right with reference to fig. Ia, and (equation 2)

Inlet flow: V_A=0 Outlet flow: V=V_A-V_B

when the piston moves to the left with reference to fig. Ib.

Please note, that the area of the piston 3 in embodiment schematically shown in fig. Ia and Ib are not equal on both sides of the piston 3. The area of the piston 3 facing volume A is the full area of the piston 3, whereas the area of the piston 3 facing volume B is lower as the rod 4 takes up some of the area. For instance if the cylinder 2 and piston 3 are cylindrical the area of the piston 3 facing volume A is fl*R² where R is the radius of the piston 3, whereas the area of the piston 3 facing volume B is π*(R-r)² where r is the radius of the rod 4.

Thus, if the diameters of the piston 3 and the piston rod are chosen so that V_A is double of the size of V_B (i.e. V_A=2*V_B), the pump 1 will pump the same amount of fluid for a given movement of the piston 3 regardless of the direction of the movement. This is very convenient if the movement of the piston 3 - or rod 4 - is used for measuring the delivered amount. When measuring the incremental of the rod, each increment will correspond to the same amount of fluid. Although the length of the stroke (the distance between positions where the movement of the piston 3 is reversed) may be considered as uncritical for measuring out the delivered amount, a clearance in the mechanism advancing the rod may introduce errors in the measuring out. Such a clearance is most pronounced when the movement of the rod changes direction whereby it is preferred to make the length of the stroke as long as possible in order to limit any error caused by clearance.

Although the above example is shown as comprising a piston reciprocating inside the cylinder, a membrane may be used instead of the piston. In such embodiments, the membrane is at it perimeter sealingly fixed to the wall of the cylinder, and the rod attached to the membrane displaces in a reciprocating manner the membrane by deforming it.

In the above example the fluid is considered to be substantially incompressible in the sense that the delivered amount corresponds to at least 95 % of the amount determined on the basis of the above geometrical relationship on displacement volumes. In the present context, pumps are preferably used for measuring out liquefied urea which is considered to be an incompressible fluid.

The configuration shown in fig. 1 has a further advantage when sealing between the piston 3 and the wall of the cylinder 2 is to be established. As indicated in fig. Ia the pressure in volume A will be lower than the pressure in volume B when the piston moves to the right. When the piston moves to the left the pressure in volumes A and B will be more or less at the same level and it will therefore in many embodiments be sufficient to provide the piston with a one way seal preventing fluid from streaming from volume B to A which seal will in general not be subjected to high pressure in the opposite direction. This makes the sealing easier. As the same type of fluid is present on both sides of the piston 3, no contamination will occur if fluid flow pass the piston, and an absolute sealing between the piston 3 and the cylinder 2 may therefore be dispensed within this and similar designs as long as it does not affect the pumping precision of the pump. A leak, i.e. flow from volume A to B pass the piston 3 and cylinder wall 2 (or vice versa), in the order of 0.01-0.05% of the pumping capacity (pumped fluid volume per hour) is typically accepted.

Fig. 2 shows schematically a cross sectional view of a pump 1 according to the present invention. The pump comprises an inlet valve 6 and an outlet valve 7. The pump 1 comprises a deformable membrane 11 being circularly shaped. The membrane is sealingly attached to a base part 12 having a void 13 being connected via channels to the inlet valve 6 and the connection valve 7. The membrane 11 is connected to a rod 4 being connected to an actuating device 29 comprising an eccentrically arranged shaft 14. Upon rotation of the shaft 14, the rod will perform a horizontal (with reference to the orientation of fig. 2a) reciprocating movement whereby the volume of the void 11 due to the elasticity of the membrane 11 will increase or decrease depending on the movement of the rod 4.

When the rod 4 moves to the right in fig. 2a, the volume of the void 11 increases whereby the inlet valve 6 opens and the connection valve 7 closes resulting in the fluid will be sucked into the void 11 if the inlet valve at its inlet is connected to a fluid reservoir. Once the rod 4 moves to the left in fig. 2a, the volume of void 11 decrease whereby the inlet valve 6 closes and the connection valve 7 opens resulting in fluid present in the void 11 will be pushed out of the void via the connection valve 7. The resulting flow profile is shown in fig. 2a. The pump shown in fig. 2a is fully workable as it is shown. However, it may be build together with a further membrane pump to form a double action pump for instance to form configurations being disclosed below in connection with figs. 4-6. This is also the case for the pump shown in fig. 3.

Fig. 3 shows schematically a pump according to the present invention. Similarly to the pump shown in fig. 2, this pump comprises valves 6, 7, a membrane 11, a base part 12, a void 13 and a rod 4. These elements are arranged and cooperate in a manner similar to what was disclosed in connection with fig. 2.

The reciprocating movement of the rod 4 is provided by an actuating device 29 comprising a cam shaft 15 with cam 16, a rod connecting plate 17 arranged rotatably by a bearing 18 which is arranged in a fixed position relatively to the base part 12. The rod 4 is rotatably connected to the rod connecting plate by a bearing 19. Furthermore, a cam cooperating wheel 20 is arranged on the rod connecting plate 17 having an axially extending surface abutting the surface of the cam 16. The actuating device also comprising a further cam mechanism implemented by a guiding surface 21 cooperating with a guide surface wheel 22 rotatably arranged on the cam shaft 15.

When the cam shaft 15 rotates in the direction of the arrow in fig. 3a, the cam 16 will push to the cam cooperating wheel 20 during some part of the rotation. This pushing action will rotate the rod connecting plate 17 in clockwise direction resulting in that the rod 4 moves to the left whereby the volume of the void 13 decreases. When the rod reaches an outermost left position, the cam 16 will no longer push to the cam cooperating wheel 20.

When this occur, the further cam mechanism 21, 22 which has been inactive during the left going motion of the rod 4 becomes active as the guide surface wheel 22 starts to abut the guiding surface 21. When the guide surface wheel 22 abuts the guiding surface 21 and the shaft 15 rotates the rod connecting plate 17 starts to rotate in a counter clockwise manner whereby the rod 4 starts to move to the right in fig. 3a.

The shaping of the cam 16 is chosen so that the rod 4 moves with a constant speed to the left resulting in a constant rate of change of the volume of the void 13 during pumping out of fluid from the void 11. The further cam mechanisms 21, 22 are shaped so that a fast sucking action is performed. The corresponding flow profile of the connection valve 7 is shown in fig. 3b and it is noted that the flow rate is constant and the time used for sucking in fluid in void 13 is substantially smaller than the time when fluid is pumped out. In many preferred embodiments the pressure at which the fluid is pumped out of the pump is considerably higher than the pressure at which fluid is sucked into the pump. For instance the outlet pressure may be 8 bars whereas the pressure at which fluid is sucked in is 1 bar. The energy used for performing a pumping cycle is proportional to the pressure times the volume pumped, and in order to optimise the use of the motor used for driving the pump it is therefore preferred to make the out-pumping stroke as long as possible and making the suction stroke as short as possible whereby a smaller motor can be used compared to a situation where e.g. the pumping stroke and the suction stroke where of equal length. In the present context a pumping stroke is considered to be the stroke where only outflow occur and the suction stroke where inflow to the pump occurs. Fig. 4a shows schematically a pump according to the present invention. The pump shown comprises two membranes 11, 23 arranged above two voids 13, 24. The two voids 13, 24 are connected to each other by connection channel 8 and the connection valve 7. The pump further comprises an inlet channel connected to the void 13 via the inlet valve 6. The voids 13, 24 are provided in a base part 12 and the membranes 11, 23 which are circular shaped are sealingly arranged at their perimeters to the base part 12.

The membranes 11, 23 are connected to one end of the rods 4, 25 respectively. At the opposite ends of the rods 4, 25 these are rotatably connected to actuating device 29. The actuating device comprises a rod connecting plate 17 by bearings 27, 28. The rod connecting plate is rotatably arranged relatively to the base part 12 at a position P along a line through the connection points of the rods 4, 25 to the base part 17 as it appears from fig. 4a. The position P determines at least to some extend the pumping characteristic of the pump and in the embodiment shown in fig. 4a, position P is chosen to be closer to bearing 27 than to bearing 28.

The actuating device further comprises a connecting rod mechanism and the connection plate 17 is connected to the connecting rod mechanism 29 having an eccentrically arranged shaft 30. Upon rotation of the shaft 30, the rod 31 will perform an up and down going motion which is transferred to the rod connecting plate 17. As the rod connecting plate 17 is rotatably arranged relatively to base part 12 at position P being closer to bearing 27 than to bearing 28 the horizontal rod 25 and 4 will move at different speeds in opposite directions - and will be displaced at different magnitudes. This means, that although the volumes of the voids 13 and 24 are equal, the displacement of the membranes 11, 23 will be different and the pump acts according to the principle outlined in equations 1 and 2. The position P is typically selected so that the ratio between displacement volumes of voids 13 and 24 is 1 :2.

The configuration of fig. 4a results in a flow out of the pump with a profile like the one shown in fig. 4b. From the flow profile it can be seen that as the position P being closer to bearing 27 than to bearing 28 an increase in volume of the void 24 will be compensated by a relatively larger decrease in volume of void 13 resulting in that the pump will be able to pump without any substantial inactive periods during a pumping cycle.

The embodiments shown in fig. 1-4 preferably comprises an incremental transducer (not shown) recording the travelling distance of the rod or rods. Such an incremental transducer may be directly recording the travelling distance of the rod(s) by detecting the movement of the rods directly or it may detect the travelling distance indirectly for instance by detecting the rotation of the shaft 30 (fig. 3 and fig. 4). In any case, the recording of the travelling distance of the rods may be used for calculating the flow out the pump by equations 1 and 2.

Fig. 5a shows schematically a further embodiment of a pump according to the present invention. The pump comprises an inlet channel 5 and an outlet channel 9 extending to outside of the pump (not shown), an inlet valve 6, a connection valve 7 and a piston 3. The piston 3 reciprocates within a cylinder 2 and this reciprocating movement is provided by the rod 4. With reference to fig. 5a, a void 24 is present above the piston 3 and a void 13 is present below the piston 3. As the rod 4 takes up some volume of void 24 the volume of void 24 is smaller than the volume of void 13 (as described in connection with fig. 1). The two voids 13 and 24 are connected by a connection channel 8 including the connection valve 7 which are arranged within the piston 3.

When the piston 3 starts to move upwards (with reference to fig. 5a) the volume of void 13 increases, the inlet valve 6 opens and fluid is sucked into void 13. At the same time, the volume of void 24 decreases, the connection valve 7 closes and fluid present in void 24 is pumped out through the outlet 9. This pumping action continues until the piston 3 reaches its upper most position at which position the flow through the pump stops until the piston 3 starts to move downwards. When the piston moves downwards the volume of void 13 starts to decrease, inlet valve 6 closes, connection valve 7 opens and the volume of void 24 increases whereby fluid will flow from void 13 to void 24 through the connection channel 8 and the connection valve 7. As the volume decrease in void 13 is faster than the volume increase in void 24 the amount of fluid flowing to void 24 is larger than the volume increase of void 24 resulting in a positive outflow from void 24 through the outlet channel 9. This continues until the piston 3 reaches its lower most position at which position no fluid will be pumped.

The rod 4 is activated by an actuating device 29 which may be in the form of an electrically driven motor or the like, and the resulting flow profile is shown in fig. 5b. In the embodiment shown in fig. 5a the actuating device 29 is a linear actuating device, such as a crank mechanism, oscillator, screw mechanism, higher movement pair or a hydraulic actuator. In particular, the actuating device 29 comprises a spindle connected with the rod 4 and an electrically driven motor (not shown), the motor is activating the spindle to provide a reciprocating movement of the rod.

Fig. 6 shows schematically a pump similar to the one shown in fig. 5a where the actuating device 29 is driven by a pressurised fluid. In a specific embodiment where the pump is used to pump urea into an exhaust system in a vehicle the pressurised fluid is taken from the power steering, coolant system, braking system, compressed air system or another source of pressurised fluid.

The pump shown in fig. 6 comprises similar features as those shown in fig. 5 and same numerals are used for similar features. The reciprocating movement of the rod 4 is provided by a servo piston 40 arranged within a servo cylinder 41. The servo piston 40 is either made integral with or attached to the rod 4 so as a movement of the servo piston 40 results in a movement of the rod 4. The volume 32 above and the volume 33 below the servo piston 40 are connectable to source of pressurised fluid 35 - in the figure indicated by a pressure pump - via a servo valve 34 and connections 36 and 37.

As it is indicated in fig. 6, the servo valve 34 has two states and in the state shown in fig. 6 fluid under pressure is pumped into lower volume 33 thereby forcing the servo piston 40 and the rod 4 upwardly. At the same time the servo valve 34 leads fluid from the upper volume 32 to a reservoir 38. When the servo piston 40 reaches its upper most position the servo valve 34 is shifted into it other position where pressurised fluid is fed to the upper volume 32 and the lower volume 33 is connected to the reservoir 38 thereby changing the direction of movement of the rod 4.

Movement of the rod 4 is recorded by an incremental transducer 8. The transducer is preferably connected to a computer and as the travelled distance of the rod 4 is directly proportional to the amount of fluid delivered through outlet channel 9 the amount of fluid delivered is easily recorded.

The servo valve 34 is also connected to a computer which is adapted to control the state of valve 34. Furthermore, the position of the servo piston 40 may also be established by recording the travelling of the rod relatively to either or both of the upper most or lower most position of the servo piston 40 whereby the computer or a mechanical controller can determine when its time to shift the state of the servo valve 34. Reset of the controlling is typically performed occasionally by letter the piston travel to one of its outer most position and the resetting the incremental transducer 39 at that position. In the embodiment shown in fig. 6 the pump will be active as long as pressurised fluid flows to the pump. In case a pulsating flow - e.g. fluid flowing out of the outlet only part time - is aimed at, this may be achieved by introducing a shut-off valve between the outlet of the valve and e.g. a nozzle arranged to receive pressurised fluid from the pressure pump. By shutting off and opening the connection between the pressure pump and nozzle, fluid will flow to the pump only when the valve is open, whereby the pump will only pump fluid as long as the shut-off valve is open. In another embodiment, the servo valve has three states where two of the states are those disclosed in fig. 6. The third state is a shut-off state where connections 36 and 37, or only one of these, are blinded. Also in this case the computer controls the state of the servo valve 34.

The present invention may find use in a number of applications and in particular in uses where atomization of a fluid is desired. One such application is for the addition of urea to the exhaust gasses of a combustion engine, such as a Diesel engine as illustrated schematically in fig. 7. The figure shows a system comprising a combustion engine 48 preferably working according to the Diesel principle, a tank 42 holding a liquid solution of urea (e.g. as known under the trade name AdBlue) and a catalytic system 43. The exhaust of the engine 48 is connected to the catalytic system 43 by an exhaust pipe 44 typically having a diameter of 120 mm, such as between 30-200 mm, which is connected to the tank 42 holding the liquid solution of urea. The system further comprises a pump 45 according to the present invention for feeding and measuring out urea into the exhaust system so that it may react with the exhaust gasses for minimisation of the discharge of NO_x gasses to the environment. The pump 45 is connected to a nozzle 37 forming one or more spray of droplets into the exhaust pipe 44.

The above disclosure has focussed on pumping urea. However, the invention is applicable of pumping other fluids as well. The invention can be fitted in or retrofitted in already existing HD-diesel engines or gas engines on trucks, buses, trains, mining equipment, construction equipment, ships airplanes.

It should be clear that the embodiments disclosed above may be amended by a person skilled in the art in many ways and still be within the scope of the present invention.

Further embodiments according to the present invention are shown in fig. 8 and 9. Fig. 8 shows a pump 1 shaped as a corbie-stepped piston device.

The pump comprising a cylinder 59 in which a corbie-stepped piston 58 is slideable arranged. The corbie-stepped shape of the piston 58 is provided by the piston part 58c whereby the area 58a is larger than the area 58b as shown in the figure. The measuring device 59 receives fluid through valve 56. The fluid is pressurised to a pressure P and is received from pressurised reservoir or a pump. The outlet of valve 56 connected to the larger displacement volume 60a of cylinder 59, and connected to the smaller displacement volume 60b of the cylinder 59 via a valve 57. The connection between the valve 57 and 5 the smaller displacement volume 60b also comprises a discharge 61 in the configuration shown in fig. 8.

Above the end of the piston part 58c opposite the end connected to the piston 58 a displacement volume 62 is provided. This displacement volume 62 receives fluid at the 10 same or substantial same pressure P as fed to the valve 56. In a preferred embodiment, the fluid supplied to valve 56 and displacement volume 62 comes from the same source.

Fig. 8 shows two modes of the pump. In the upper part of fig. 8, valve 56 is open and valve 57 is closed whereby fluid at pressure P streams towards the larger displacement

15 volume 60a. As the area of the top of the piston part 58c is smaller than the area 58a and the pressure in displacement volumes 60a and 62 are equal, the piston 58 will be displaced to the right with reference to fig. 8. The right-going movement results in that fluid present in displacement volume 60b is pressed out through the discharge 61. This action continues until the piston 58 reaches its right-most position at which position valve 56 is closed and

20 57 is opened; this situation is disclosed in lower part of fig. 8.

When valve 56 is closed and valve 57 is open, the pressure in displacement volume 62 will push the piston 58 to the left with reference to fig. 8. Fluid present in displacement volume 60a will flow out, through the valve 57 and into the displacement volume 60b as well as 25 out through the discharge 61. This left-going action continues until the piston 58 reaches its left-most position, when the states of the valves 56 and 57 are both changed and the cycle repeats.

The embodiment of fig. 8 has among other advantages that the delivery is present except 30 at the left-most and right-most positions of the piston and that the pressure of the fluid delivered to the discharge 61 is well defined. Furthermore, a strong geometrical relationship is present between the amount of fluid delivered through discharge 61 and the movement of the piston part 58c.

35 The size of the areas 58a and 58b may be selected so that the same amount delivered to the discharge irrespective of the way the piston 58 moves. This may be achieved when the size of area 58a is twice the size of area 58b. Furthermore, the sizes of the displacement volumes have the following ratio 2: 1 : 1 (60a:60b:62). Embodiments like the one shown in fig. 8 has the further advantages that the direction change of the piston 58 can be performed very quickly and thereby only little interruption in fluid delivery is present (the directional change is typically governed by the speed at which the state of the valves can be changed). In other embodiments where a suction stroke is present the interruption is comparable larger. 5

By arranging the valves 56 and 57 as indicated on fig. 8 redirection valves are not needed and the relatively simpler shut-off valves may be applied.

Fig. 9 shows an embodiment similar to the embodiment of fig. 8. Features of the 10 embodiment shown in fig. 9 which are similar to features shown in fig. 8 have been labelled with the same numerals. Similarly, the upper part of fig. 8 shows a situation where the piston 58 moves to the right, and the lower part shows a situation where the piston moves to the left.

15 In the embodiment of fig. 9, sealing membranes 63a and 63b are provided between the piston 58 and the displacement volume 60a and between the piston part 58c and the displacement volume 62. The presence of the sealing membranes 63a and 63b provides a seal hindering fluid from flowing between the volumes 60a and 60b pass the edge of the piston 58.

20

Fig. 10 shows a further embodiment of a pump according to the present invention. The pump comprising a piston 76 having piston heads 63 and 64. The piston heads 63, 64 abuts membranes 65 and 66 respectively. The displacement volumes of the pump are labelled 67 and 68 respectively. The piston 76 is rotatably arranged on a rod 72 which is

25 rotatably arranged by a bearing 75 and activated by an activating device in the form of a cam shaft 74.

When the piston 64 moves downwardly with reference to fig. 10, fluid is sucked through valve 70 into the displacement volume 67. In consequence of the sucking action, the valve

30 71 closes. Fluid present in displacement volume 68 will be pressed out through the channel 69. When the piston moves upwardly with reference to fig. 10, fluid present in displacement volume 67 will be pressed out resulting in that valve 70 closes and valve 71 opens. Furthermore, the volume of displacement volume 68 will increase whereby at least a part of the fluid flowing out of displacement volume 67 will flow into displacement

35 volume 68.

The cam 74 is arranged to provide a flow profile similar to the one disclosed in connection with fig. 5b. The membrane 65 is designed to provide an optimal suction action whereas the membrane 66 is a flat disc made from rubber. Even though, the present description has focused on different embodiments each having distinct features it should be emphasised that features disclosed in connection with one embodiment is applicable in connection with another embodiment.

Claims

1. A pump comprising a first and a second void (13, 24), the volumes of the voids are de-/increasable thereby each having a displacement volume and being in fluid communication with each other via a one way valve connection valve (7) allowing fluid to flow from the first void and to the second void only, the first void comprising an inlet for receiving fluid from a fluid source and the second void comprising an outlet for delivery of fluid, - a one way inlet valve (6) connected to the first void (13) and allowing fluid to flow into the first void only, an actuating device adapted to de- and increasing the volumes of the voids so as to provide as pumping of fluid through the pump.

2. A pump according to claim 1, wherein the volumes of the voids (13, 24) are de-

/increasable interdependent of each other in such a manner that when one of the volumes decreases the volume of the other void increases.

3. A pump according to claim 1 or 2, wherein the ratio between the displacement volumes of the voids is 1 :2, the first void having the largest displacement volume.

4. A pump according to any of the preceding claims, comprising a piston (3) or a membrane and a cylinder (2), the membrane is at its perimeter sealingly attached to the cylinder, wherein the piston (3) or membrane is reciprocatable arranged in the cylinder and the first void is on one side of the piston and the second void is on the other side of the piston.

5. A pump according to claim 4, wherein the first and the second void (13, 24) is connected via a connection channel (8) including the connection valve (7).

6. A pump according to claim 5, wherein connection channel (8) including the connection valve (7) is arranged within the piston (3).

7. A pump according to claim 5, wherein the connection channel (8) including the connection valve is arranged outside the cylinder (2).

8. A pump according to any of the preceding claims 4-7, wherein the piston (3) is connected via a rod (4) to an actuating device (29) for imposing a reciprocating movement to the piston (3).

9. A pump according to claim 8, wherein the actuating device is driven by pressurised fluid.

10. A pump according to claim 9, wherein the pump comprises a servo valve (34) and the 5 actuating device (29) comprises a servo cylinder (41) and a servo piston (40), the servo valve (34) being adapted to lead pressurized fluid to one side of the servo piston (40) and open a connection from the other side of the servo piston (40) to a reservoir (38) or vice versa to provide to establish a reciprocating movement.

10 11. A pump according claim 9 or 10, wherein the servo valve (34) is connected to a source of pressurised fluid, the source providing pressurized fluid to other means, such as a braking system, air suspension system for a vehicle or the like.

12. A pump according to 8, wherein the actuating device comprising a spindle connected 15 or made integral with the rod and an electrically driven motor, the motor is activating the spindle to provide a reciprocating movement of the rod.

13. A pump according to any of the claims 1-3, wherein each void (13, 24) comprises an open ended cavity having its open end closed by a deformable membrane (11, 23).

20

14. A pump according to claim 13, wherein the first and the second void (13, 24) is connected via a connection channel (8) including the connection valve (7).

15. A pump according to claim 13 or 14, wherein each membrane is connected to a rod (4) 25 connected to an actuating device (29) for introducing a reciprocating movement of the rod.

16. A pump according to claim 15, wherein the actuating device (29) comprising a rotatably arranged rod connecting plate (17) and a first cam mechanism providing movement of one of the rod in a first direction and a second cam mechanism providing

30 movement of the other rod in an opposite direction.

17. A pump according to any of the preceding claims, wherein the actuating device is adapted to provide a flow out of the out during at least 90 % of a pumping cycle.

35 18. A pump according to claim 17, wherein the flow out of the pump is substantial constant, e.g. the difference between maximal and minimum flow rate is within 5 % of the average flow rate during a pumping cycle.

19. A pump according to any of the preceding claims, further comprising an incremental transducer (39) measuring either directly or indirectly the travelling distance of the rod or rods.

20. A pump comprising a void (13), the volume of the void is de-/increasable thereby having a displacement volume, a one way inlet valve (6) connected to the void (13) and allowing fluid to flow into the void only via the inlet valve and a one way connecting valve (7) allowing fluid to flow out of the void only via the connecting valve (7), an actuating device adapted to de- and increasing the volumes of the voids so as to provide as pumping of fluid through the pump.

21. A pump according to claim 20 comprising one or more of the features disclosed in claims 1-19.

22. A system for administrating fluid, preferably liquefied urea, into an exhaust system of a vehicle, the system comprising a pump according to any of the preceding claims, a fluid reservoir connected to the inlet of the pump and a nozzle connected to the outlet of the pump, wherein the nozzle is arranged in the exhaust system so as to atomize and spray the thereby formed droplets into the exhaust system.

23. A method of measuring out liquefied urea, the method comprising using a pump according to any of the preceding claims 1-21 or a system according to claim 22, which pump being at its inlet connected to a reservoir of liquefied urea and at its outlet connected to a nozzle.

24. A method according to claim 23, comprising transforming a determined demand for a given amount of liquid supplied by the pump into a de-/increase of the volume(s) of the void(s) and activating the actuating device to provide the de-/increase of the volume(s) so as to provide the demanded amount of liquid.