WO2017065685A1

WO2017065685A1 - Membrane fluid pump

Info

Publication number: WO2017065685A1
Application number: PCT/SE2016/051002
Authority: WO
Inventors: Daniel OTTOSEN; Gunnar Skarping; Marianne Dalene
Original assignee: Provtagaren AB
Current assignee: Provtagaren AB
Priority date: 2015-10-15
Filing date: 2016-10-17
Publication date: 2017-04-20
Anticipated expiration: 2018-04-15
Also published as: US20180306170A1; EP3380731A1; EP3380731A4

Abstract

The invention relates to a membrane fluid pump(1), comprising a drive shaft (2) rotatable within the membrane fluid pump. The shaft is equipped with a number of eccentrics (7) arranged axially along the shaft(2). The membrane fluid pump further comprises a set of connecting rods(3, 4)being connected to each of the eccentrics(7), where in each connecting rod (3, 4) is attached between one of the eccentrics (7) on the shaft (7) and a membrane (3'', 4''), so that each of the connecting rods(3, 4)is arranged to transfer a rotating movement of the shaft (2) to a reciprocating movement pattern of each the membrane(3'', 4''). Each of the eccentrics (7) and the connecting rods (3, 4)are arranged in such a manner that all of the membranes (3'', 4'') will reciprocate with a phase shift evenly distributed over a 360 degree rotation of the drive shaft(2), and wherein all of the eccentrics (7) are rotationally offset to each other with an angle so that they are evenly distributed over a 360 degree rotation of the drive shaft(2).

Description

MEMBRANE FLUID PUMP

Technical field

The present invention relates generally to membrane fluid pump. More particularly, the present invention relates to a membrane pump as defined in the introductory parts of claims 1 .

Background art

In air sampling scenarios for different pollutants and different analysis methods, the air flow rate through the samplers is important for the

performance of a correct measurement with a sampler. To provide a reliable air flow membrane pumps are often used. Different sampler types, however, often require different flow rates. For the membrane pump to function with different sampler types the pump will thus need to operate with different speed.

A normal membrane pump has two membranes, each membrane being driven by a separate connecting rod. The connecting rods for the two membranes are often driven by a common drive shaft with a cam

arrangement so that the membranes will be driven with a phase shift of 180 degrees to each other so that they will produce a fairly even flow rate. The two connecting rods are often connected to a single eccentric resulting in heavy vibrations in the pump.

The reciprocating nature of connecting rods in a membrane pump will lead to vibrations in the pump and an uneven torque for the motor driving the connecting rods. Vibrations and an uneven load for driving the membrane pump will wear the pump so that service will be required on a regular basis. Vibrations will also affect the sampling negatively if the vibrations reach the sampler. The motor driving the pump will also be affected by the vibrations and need service or replacement at a regular basis. The motor will further be negatively influenced by the uneven load from the membrane pump leading to decreased lifetime of the motor. A solution to solve the vibrational problems of traditional membrane pumps is suggested in CN210326534Y, where a pump with eight membranes configures in two levels is presented. All membranes are driven by pistons connected to a common drive shaft with a cam profile controlling the phase of the membranes. Each level with four membranes are driven by the drive shaft to pump during with two membranes at a time 90 degrees phase shifted. The cam shape of the drive shaft is made so that each opposing pistons will be in their outer and inner positions, respectively, at the same time, thereby balancing/neutralizing the mass movements of the pistons. The lower level is an exact copy of the upper level.

A drawback with the configuration of CN210326534Y is that only two pulses per revelation of the drive shaft is achieved by the eight membranes and eight pump chambers. The two pulses are further produced during the first 180 degrees of a piston revolution. A vibration free movement is thus achieved on the expense of a very uneven flow. The cam shape of the drive shaft and will also inflict a very uneven load for the pump engine reducing energy efficiency of the pump. The pistons in CN210326534Y are further fastened in the drive shaft by rigid ring bearings, producing a movement where the piston angle is changed radically during each piston reciprocation.

There is thus a need for an improved membrane fluid pump that vibrates less during operation to avoid disturbing measurements and reducing the need for service and that is easier to drive.

Summary of the invention

It is an object of the present invention to improve the current state of the art, to solve the above problems, and to provide an improved membrane fluid pump producing less vibrations and being easier to drive. These and other objects are achieved by a membrane fluid pump, comprising a drive shaft rotatable within said fluid pump. The shaft is equipped with a number of eccentrics distributed axially along the shaft. The membrane fluid pump further comprises a set of connecting rods being connected to each of the eccentrics, wherein each connecting rod is attached between one of the eccentrics on the shaft and a membrane, so that each of the connecting rods is arranged to transfer a rotating movement of the shaft to a reciprocating movement pattern of each of the membranes. Each connecting rod and corresponding membrane operates in an individual pump chamber. Each of the eccentrics and the connecting rods are arranged in such a manner that all of the membranes will reciprocate with a phase shift evenly distributed over a 360 degree rotation of the drive shaft, and all of the eccentrics are rotationally offset to each other with an angle so that they are evenly distributed over a 360 degree rotation of the drive shaft.

By driving different eccentrics with offset angle evenly distributed over 360 degrees (e.g. 0 and 180 degree for 2 eccentrics) the mass movement in the radial direct to the drive shaft of the first set of connecting rods is the opposite to the second set of connecting rods. The centre of mass in the radial direction to the crank shaft is thus constant during the movement of the connecting rods and thereby the membranes. This leads to a vast reduction in vibrations compared to normal membrane pumps with only one eccentric and one set of connecting rods. Since all membranes reciprocate in succession with a phase shift that is evenly distributed over 360 degrees, the heavy pulsation characteristic to membrane pumps is greatly reduced. Also the load for the engine is evenly distributed, reducing the energy needed to drive the pump.

The membrane fluid pump will due to the large number of membranes have a redundancy. If one membrane fails, others will still work as long as the membrane valve is closed.

The membrane pump according to the invention each eccentric may have three connecting rods attached, each connected to one membrane. In that way the membrane pump may be driven by a three phase electrical motor simplifying acquisition of a motor for driving the pump. This motor may be equipped with a rotary encoder, such as a set of Hall sensors in order to measure and control motor speed. It is further an advantage to enable to use standardized electrical motors if the motor has to be replaced, making it easier and cheaper to find a new motor.

The shaft of the membrane fluid pump may be equipped with two eccentrics, wherein each of the two eccentrics is connected to a set of three connecting rods. By offsetting the two eccentrics by 180 degrees the membranes will reciprocate with a successive phase shift of 60 degrees while at the same time constantly keeping an unchanged mass balance in the radial direction of the drive shaft reducing vibrations and keeping a constant load for driving the pump.

According to other embodiments of the invention the shaft may be equipped with more than two eccentrics, and the number of connecting rods connected to each eccentric is one more than the number of eccentrics. The shaft may be equipped with more than two eccentrics, and the number of connecting rods connected to each eccentric is one less than the number of the eccentrics. The same advantages are achieved with successive

membrane movements evenly distributed over 360 degrees while keeping mass balance during operation.

The membrane fluid pump according to the present invention may however in other embodiments comprise each eccentric to have more than three connecting rods attached. The same advantages as for the

embodiments already discussed are achieved also with sets of connecting rods having e.g. five connecting rods and five 5 membranes. The advantage with having a greater number of connecting rods and membranes is further that the flow rate will be smoother as the cycles of each connecting rod and membrane will have a smaller phase shift to the next connecting rod and membrane. With five connecting rods connected to an eccentric, the connecting rods will have a phase shift of only 72 degrees compared to 120 degrees when having three connecting rods connected to an eccentric.

It is further preferred that the sets of connecting rods connected to each eccentric are arranged to reciprocate from the same axial position along the drive shaft. Each of the sets of connecting rods may e.g. be fastened to a ball bearing enveloping the eccentric of the drive shaft so as to create a crank effect. If the connecting rods are evenly distributed around the circular ball bearing, the phase shift between neighbouring connecting rods will be 360 degrees divided by the number of connecting rods.

According to a still further embodiment of the present invention the membrane fluid pump comprises a drive shaft rotatable within the fluid pump, a number of sets of connecting rods attached to the drive shaft so as to reciprocate with a phase shift evenly distributed over a 360 degree rotation of the drive shaft, wherein each connecting rod is arranged to drive a separate membrane. The number of sets of connecting rods is equal to the number of connecting rods in each set, and each set of connecting rods are driven out of phase in relation to each other with 360 degrees divided by the number of sets of connecting rods. The number is greater than two. In this embodiment each connecting rods will operate in phase with one connecting rod in each connecting rod set, where the connecting rods that operate in phase will have a phase shift evenly distributed over 360 degrees. In that way the centre of mass in the radial direct will stay unaffected by the crank movements leading to a vibration free operation of the membrane fluid pump.

The membrane fluid pump of the invention may further comprise an inlet valve and an outlet valve for each membrane. The inlet valve and outlet valve are opening and closing by the difference in fluid pressure the said membrane exerts when moving in a reciprocating pattern. If several membrane inlets and outlets are connected in a manner so that the fluid pressure change from each of said reciprocating membrane contributes to the opening and closing mechanism of said inlet and outlet valves. Prior art membrane pumps may have pressure difference driven inlet and outlet valves which are in an undefined state when no pressure difference is present. A certain pressure difference threshold is required to put those valves in either open or closed state, therefore a certain membrane reciprocating speed is required before such a pump will operate properly. A pump with normally closed valves will be able to operate at much lower membrane reciprocating speed enabling lower flow rates.

According to a further embodiment of the present invention the shaft of several pump modules are connected in series, increasing the number of total membranes, thereby either further increasing total flow and reducing the pulsation if the membranes are evenly phase shifted among the modules or connecting several membranes in series, achieving a several stage vacuum pump or compressor. The shaft may further be equipped with a gearbox to control the speed of the shaft and to reduce the rotational speed range of the motor driving the shaft.

The flow rate of the membrane fluid pump may further be controlled by enabling and disabling the opening and the closing of valves of separate membranes. A control unit connected to the pump controlling the valves will thereby be able to effectively control the flow of the membrane fluid pump. The flow rate of the membrane fluid pump may further be controlled by changing the offset of the eccentrics thereby changing the displacement volume of each membrane stroke. If a membrane is broken, the phase shift between the remaining membranes may be controlled so that the strokes of the remaining membranes are evenly distributed over a rotation and thereby produces a pulse-free flow. The change may either be semi-permanently made when assembling the pump at the manufacturing stage or the eccentrics may be arranged to be controlled so as to change the

displacement volume by e.g. changing the angle that the connecting rod is attached to the eccentric. The flow rate of the membrane fluid pump may further be controlled by changing the dead volume of the membrane cavity.

According to a further embodiment of the invention the inlets and/or outlets from all membranes of the membrane fluid pump are interconnected via a cavity, so as to reduce interference between pump heads. A pump head comprises a reciprocating membrane connected to a cavity further connected to an inlet valve and an outlet valve, where said membrane inflates said cavity while said inlet valve is open and deflates said cavity while said outlet valve is open.

As presented above, the problems of the prior art are thus addressed by the fluid membrane pump of the present invention. A vibration free operation of the membrane fluid pump is facilitated due to a centre of mass in the radial direction of the drive shaft that does not change during operation. This also leads to a membrane fluid pump that is easier and smoother to drive for a drive motor. A pulse free flow is also achieved since the reciprocating movements of the membranes are phase shifted evenly distributed over a rotation. Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [element, device, component, means, step, etc.]" are to be interpreted openly as referring to at least one instance of said element, device, component, means, step, etc., unless explicitly stated otherwise.

Brief description of the drawings

The above objects, as well as additional objects, features and advantages of the present invention, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, when taken in conjunction with the accompanying drawings, wherein: Fig. 1 is schematic view of the cross section of one of the sets of connecting rods of a membrane fluid pump according to the present invention.

Fig. 2 is schematic view of a cross section along the drive shaft of the membrane fluid pump of the present invention showing the principle of the invention.

Fig. 3 is perspective view showing two neighbouring connecting rods in the direction of the drive shaft. The two visible connecting rods belong to two different connecting rod sets.

Fig. 4a is a representation of the pulsation of the output flow from a pump according to the prior art. Fig. 4b is a representation of the pulsation of the output flow from the pump according to Fig. 2 and Fig. 3. Fig. 5 is table showing different possible configurations for an optimized multi membrane pump according to the invention.

Detailed description of preferred embodiments of the invention

Fig. 1 is schematic view of the cross section of one of the sets of connecting rods 3, 4 of a membrane fluid pump 1 according to the invention. The connecting rods 3, 4 reciprocate with a phase shift evenly distributed over a 360 degree rotation of the drive shaft 2. As there are three connecting rods 3, 4 in the embodiment of Fig. 1 , the individual connecting rods 3, 4 with their respective membranes 3", 4" will be phase shifted 120 degrees apart from each other. Each connecting rod 3, 4, of the set of connecting rods 3, 4 is arranged to drive a separate membrane 3", 4". The connecting rods 3, 4 of the set of connecting rods 3, 4 are fastened to an eccentric 7 offset to drive shaft 2. The connecting rods 3, 4 are evenly distributed around the

circumference of the eccentric to accomplish a reciprocating movement for each connecting rod 3, 4 phase shifted 120 degrees to the next.

Fig. 2 shows the membrane pump 1 of the present invention in a cross section along the drive shaft 2 showing the principle of the invention with having two connecting rod sets 3, 4 arranged to actuate their respective membranes 3", 4" in counter phase to each other, i.e. with a phase shift of 180 degrees. The drive shaft is connected to a motor 8 for driving the pump. As can be seen in Fig. 2 when one connecting rod 3 of one connecting rod set is in its upper end position upwards, the neighbouring connecting rod 4 in the direction of the drive shaft 2 is in its lower end position thereby eliminating any the combined mass movement in the radial direction to the drive shaft 2.

The connecting rods 3, 4 of each of the first set of connecting rods 3 and the second set of connecting rods 4 are arranged to reciprocate from the same position along the length of said drive shaft but phase shifted 180 degrees to eliminate any average mass movement in the radial direction of the drive shaft. Fig. 2 further shows the motor 2 driving the membrane fluid pump. The skilled person realizes from the claims and the summary of the invention that the embodiment of Fig. 2 could be extended with further sets of connecting rods. Any number of sets of connecting rods attached to the drive shaft may be arranged to reciprocate with a phase shift evenly distributed over a 360 degree rotation of the drive shaft. Each connecting rod is arranged to drive a separate membrane, and the number of sets of connecting rods is then chosen to be equal to the number of connecting rods in each set of connecting rods. If the different sets of connecting rods are driven out of phase in relation to each other with 360 degrees divided by said number of sets of connecting rods the average mass movement in the direction of the drive shaft will be eliminated.

Fig. 3 is perspective view showing two neighbouring connecting rods 3, 4in the direction of the drive shaft 2 of the fluid membrane pump 1 . The two visible connecting rods belong to two different connecting rod sets attached to two different eccentrics 7. The membranes (not shown) are placed over the holes 5, 6 and are driven by the connecting rods 3, 4 in counter phase to each other to eliminate any average mass movement in the radial direction to the drive shaft. Fig. 3 reveals a further advantage of the present invention. All chambers angled in the same direction, in the configuration of Fig. 2 and Fig. 3 two of the six chambers, may be serviced by removing one single "cylinder head" or lid.

Fig. 4a shows a representation of the pulsation of the output flow from a pump according to the prior art. The solid lines show the pulses induced by the eight membranes of CN210326534Y, while the dashed line represent the combined average flow. Fig. 4b shows the pulsation of the output flow from the pump according to Fig. 2 and Fig. 3. As can be seen the pulsation is much smother from the pump according to the present application than from the prior art pump. The reason for this is that the membranes of

CN210326534Y only pump at 90 and 180 degrees, leaving half a revolution of the crank shaft without any induction of pulses by the membranes.

Fig. 5 shows different possible embodiments of the pump according to the present invention. The possible embodiments are marked in the table with a box and grey background. All the combinations of the table would produce a functioning pump, but only the combinations marked with a box and grey background achieve all advantages of the invention, i.e. a pulsation free pump where the reciprocation of the pistons and membranes are neutralized so that no net mass movement is present during rotation. In other words, the centre of mass is always kept along the centre axis of the drive shaft 2 during operation of the pump. Fig. 5 shows that this configuration is possible with

- three rods per eccentric and two eccentrics,

- four rods per eccentric and three eccentrics, and

- five rods per eccentric and four eccentrics.

The advantages shown above in accordance with the invention is thus achieved by a pump according to what is described above having N rods and

N-1 eccentrics, when N>3.

It is understood that other variations in the present invention are contemplated and in some instances, some features of the invention can be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly in a manner consistent with the scope of the invention.

Claims

1 . Membrane fluid pump (1 ), comprising

a drive shaft (2) rotatable within said membrane fluid pump,

a number of eccentrics (7) arranged axially along the shaft (2), a set of connecting rods (3, 4) being connected to each of said eccentrics (7), wherein each connecting rod (3, 4) is attached between one of said eccentrics (7) on said shaft (7) and a membrane (3", 4"), so that each of said connecting rods (3, 4) is arranged to transfer a rotating movement of said shaft (2) to a reciprocating movement pattern of each said membrane (3", 4"), wherein each of said eccentrics (7) and said connecting rods (3, 4) are arranged in such a manner that all of said membranes (3", 4") will reciprocate with a phase shift evenly distributed over a 360 degree rotation of said drive shaft (2), and

wherein all of said eccentrics (7) are rotationally offset to each other with an angle so that they are evenly distributed over a 360 degree rotation of said drive shaft (2).

2. Membrane fluid pump according to claim 1 , wherein said shaft (2) is equipped with one or several eccentrics (7), wherein each of said eccentrics

(7) is connected to a set of one or several connecting rods (3, 4).

3. Membrane fluid pump according any one of the preceding claims, wherein the connecting rods (3, 4) of each of said set of connecting rods (3, 4) are arranged to reciprocate from the same axial position of said drive shaft (2).

4. Membrane fluid pump according to any one of the preceding claims, wherein each of said eccentrics (7) has a bearing that can typically be a ball or a sleeve bearing between said shaft (2) and said connecting rods (3, 4) attached to that eccentric (7).

5. Membrane fluid pump according any one of the preceding claims, further comprising a pump head consisting of an inlet valve and an outlet valve or a valve combining inlet and outlet functionality for each pump.

6. Membrane fluid pump according to claim 5, where said each inlet valve and outlet valve are opening and closing by the fluid flow that the said membrane (3, 4) induces when moving in a reciprocating pattern.

7. Membrane fluid pump according to claim 5, where said each inlet valve and outlet valve are opening and closing as an active mechanism

8. Membrane fluid pump according to claim 5, where said each inlet valve and outlet valve are opening and closing by a predetermined pressure difference threshold.

9. Membrane fluid pump according to claim 8, where several membrane inlets and outlets are connected in a manner that the fluid pressure change each of said reciprocating membrane contributes to the said opening and closing mechanism of said inlet and outlet valves.

10. Membrane fluid pump according any one of the preceding claims, wherein the shaft (2) of several pump modules are connected in series, increasing the number of total membranes.

1 1 . Membrane fluid pump according any one of the preceding claims, wherein the shaft connection is equipped with a gearbox, making it possible for said shafts connected in series to have different rotational speeds.

12. Membrane fluid pump according any one of the preceding claims, wherein the flow rate of the membrane fluid pump is arranged to be controlled by enabling and disabling opening valves and closing valves of separate membranes.

13. Membrane fluid pump according any one of the preceding claims, wherein the flow rate of the membrane fluid pump is arranged to be controlled by changing the offset of the eccentrics thereby changing the displacement volume of each membrane stroke.

14. Membrane fluid pump according any one of the preceding claims, wherein the flow rate of the membrane fluid pump is arranged to be controlled by changing the dead volume of the pump head cavity.

15. Membrane fluid pump according any one of the preceding claims, wherein the inlets and/or outlets from all membranes are interconnected via a cavity, so as to reduce interference between opening and closing of inlet valves and outlet valves in said pump heads.