Patent Application
20080101970
The present invention relates to delivering liquid at a high pressure at which compressibility of the liquid becomes noticeable.
The EP 0 309 596 B1 discloses a pumping apparatus for delivering liquid at a high pressure at which compressibility of the liquid becomes noticeable. The known pumping apparatus comprises a first actuator for actuating a first reciprocation piston for pumping at least a part of the fluid and a second actuator for actuating a second reciprocation piston for pumping at least a part of the fluid. The known pumping apparatus also comprises a main drive coupled to the first actuator and to the second actuator.
In the known apparatus the coupling between the drive and the actuators is adapted for driving the actuators with different velocities such that the pistons have different stroke lengths between the respective top dead center and the respective bottom dead center. The apparatus is provided with a controller coupled to the drive for adjusting the stroke lengths of each of the pistons. This adjustment depends on the desired flow rate of the liquid delivered by the pumping apparatus, wherein the stroke volume, i.e. the amount of liquid displaced during a pump cycle, being decreased when the flow rate is decreased and vice versa. With help of such an adjustment pulsations in the flow of the liquid delivered by the pumping apparatus can be reduced.
It is an object of the invention to provide an improved delivering of liquid at a high pressure at which compressibility of the liquid becomes noticeable. The object is solved by the independent claims. Preferred embodiments are shown by the dependent claims.
In order to see how the provision of a variation of a phase relationship between reciprocating motions of the pistons leads to a reduction in the flow pulsations the following is to be considered:
In known pumping apparatuses the drive is coupled to the actuators for providing a predetermined and fixed phase relationship between the reciprocating motions of the pistons. If the apparatus comprises for example two pistons, the two pistons have a phase relationship such that the two pistons always move in opposite directions and never move in the same direction. Accordingly, if the one piston performs its pumping stroke the other piston performs its suction stroke and vice versa. At the beginning of each pumping stroke, i.e. at the bottom dead center of the respective piston, the requested high pressure has to be built-up within a chamber in which the respective piston moves. Due to the noticeable compressibility of the liquid the piston needs a recognizable time for building up the requested high pressure. At the same time the other piston is at the beginning of its suction stroke, i.e. at its top dead center. Due to the noticeable compressibility of the liquid the pressure in a chamber, in which this piston moves, falls according to its elasticity and compressible volume content. Accordingly, the changes between suction strokes and pumping strokes of the pistons result in pulsations in the flow of the liquid delivered by the pumping apparatus. By varying the phase relationship between the reciprocating motions of the pistons it is possible e.g. to timely set the beginning of the pumping stroke of the one piston for building up the high pressure in the respective chamber during a period of time in which the other piston still performs its pumping stroke producing the high pressure in the respective chamber. Accordingly, for a short transition period of time both pistons simultaneously are performing forward pumping strokes.
According to embodiments of the invention the phase relationship between the reciprocating motions of the pistons can be varied by timely shifting a top dead center of one of the pistons to a later time or, alternatively, by timely shifting a bottom dead center of one of the pistons to an earlier time. By timely shifting the top dead center of one of the pistons to a later time the respective piston performs a timely enlarged pumping stroke allowing the other piston to build up the high pressure at the beginning of its own pumping stroke. Alternatively, the time shift of the bottom dead center of the one of the pistons to an earlier time allows the respective piston to build up the high pressure in its chamber before the other piston arrives at the end of its pumping stroke.
According to embodiments of the invention, each actuator comprises a spindle drive comprising a spindle having an external thread and being drive coupled to the main drive, and a nut having an internal thread and being drive coupled to the respective piston. One of these nuts is torque proof guided parallel to the longitudinal extension of the respective spindle by a guiding. The phase shifter comprises an auxiliary drive coupled to the other of the nuts such that the respective nut is moveable parallel to the longitudinal extension of the respective spindle. The respective spindle drive converts a rotary movement of the main drive into a longitudinal movement of the respective piston. By using the auxiliary drive a conversion rate between incoming rotary movements and outgoing longitudinal movements is adjustable within the spindle drive to which the auxiliary drive is assigned to. In particular, the auxiliary drive allows timely shifting the top dead center and the bottom dead center of the piston assigned to the nut which is coupled to the auxiliary drive.
Other objects and many of the attendant advantages of embodiments of the present invention will be readily appreciated and become better understood by reference to the following more detailed description of embodiments in connection with the accompanied drawings. Features that are substantially or functionally equal or similar will be referred to by the same reference signs.
According to
The pumping apparatus 2 comprises an inlet valve 5, controlling an inlet pipe 6. In this embodiment said inlet valve 5 can be closed and opened by a solenoid 7 under the control of a controller or control circuitry 8.
The pumping apparatus 2 comprises at least two pumps, namely a first pump 9 and a second pump 10. For each pump 9, 10 the pumping apparatus 2 comprises a respective actuator, namely a first actuator 11 for driving the first pump 9 and a second actuator 12 for driving the second pump 10. Although, the embodiment depicted in the
Each pump 9, 10 comprises a piston, namely a first piston 13 and a second piston 14, and a chamber, namely a first chamber 15 and a second chamber 16. The pistons 13, 14 are adapted for reciprocating movements inside of the respective chamber 15, 16. The pistons 13, 14 could be made of sapphire. The respective chamber 15, 16 is provided within a housing, namely a first housing 17 comprising the first chamber 15 and a second housing 18 comprising the second chamber 16.
The first chamber 15 is connected to the inlet port 3 by the inlet pipe 6. The first chamber 15 is also connected to the second chamber 16 by a connecting pipe 19 and the second chamber 16 is connected to the outlet port 4 by an outlet pipe 20. The connecting pipe 19 is provided with an outlet valve 21, which can be e.g. a conventional check valve closing in the direction from the second chamber 16 to the first chamber 15. The outlet pipe 20 can be provided with a damping unit 22 which serves for damping any pressure and flow variations which may occur in the outflow of the second pump 10.
In the preferred embodiments depicted in the
In the depicted preferred embodiments each actuator 11, 12 comprises a spindle drive, namely a first spindle drive 23 and a second spindle drive 24. Each spindle drive 23, 24 comprises a spindle, namely a first spindle 25 and a second spindle 26 each having an external thread 27, and a nut, namely a first nut 28 and a second nut 29 each having an internal thread, which is not shown and which is formed complementary to the external thread 27 of the respective spindle 25, 26. Preferably, the respective spindle drive 23, 24 is a ball-screw spindle drive having a ball (not shown) rolling in the threads 27 of the respective spindle 25, 26 and of the respective nut 28, 29.
The pumping apparatus 2 comprises a main drive 30 adapted for driving the actuators 11, 12. The main drive 30, which preferably is an electromotor, is drive coupled to the inlet sides of the actuators 11, 12. The inlet side of each actuator 11, 12 is represented by its spindle 25, 26. The main drive 30 is coupled to the actuators 11, 12 by a gear 31, comprising several gear wheels, namely a first gear wheel 32 torque proof connected to the first spindle 25, a second gear wheel 33 torque proof connected to the second spindle 26 and a third gear wheel 34 torque proof connected to a shaft 35 of the main drive 30. The gear wheels 32 to 34 are mating for drive coupling the main drive 30 to the actuators 11, 12. The main drive 30 induces a rotary movement in to the gear 31 and therefore into the spindles 25, 26. Said rotary movements are symbolized by arrows 36.
Each spindle drive 23, 24 converts the incoming rotary movement into a longitudinal movement of the respective nut 28, 29 represented by arrows 37. The actuators 11, 12 are drive coupled to the respective pistons 13, 14 via balls 38 arranged in corresponding ball receptions 39. Each ball 38 is contacted to a piston holder 40 supporting the respective piston 13, 14. The pistons 13, 14 are also provided via their piston holders 40 with return springs 41. Each return spring 41 is connected at one of its ends to the respective housing 17, 18 and at its other end to the respective piston holder 40. The return springs 41 are biasing the piston holder 40 and therefore the respective piston 13, 14 towards the respective actuator 11, 12.
According to the embodiments depicted in the
In operation of the main drive 30 the pistons 13, 14 perform reciprocating movements within the respective chambers 15, 16. Each piston 13, 14 performs alternately pumping strokes and suction strokes. During such a pumping stroke the respective piston 13, 14 moves with its front end 45 or 46, respectively, from its bottom dead center towards a front wall 47 or 48, respectively, of the respective chamber 15, 16 to its top dead center. During each pumping stroke the respective piston 13, 14 reduces the volume of the respective chamber 15, 16 and presses liquid out of the respective chamber 15, 16. During each suction stroke the respective piston 13, 14 moves with its front end 45, 46 from its top dead center to its bottom dead center away from the front wall 47, 48 of the respective chamber 15, 16. During said suction stroke the volume of the respective chamber 15, 16 is enlarged and the respective chamber 15, 16 is filled with liquid. Between the reciprocating movements of the two pistons 13, 14 is established a phase relationship such that the two pistons 13, 14 mostly move contrariwise. In other words, when the one piston 13 or 14 performs its pumping stroke the other piston 14 or 13 essentially performs its suction stroke and vice versa. In a conventional pumping apparatus, for example known from previously cited EP 0 309 596 B1 the phase relationship between the movements of the pistons 13, 14 is invariantly fixed such that the two pistons 13, 14 never move in the same direction. The two pistons 13, 14 accordingly have a fixed phase relationship between their reciprocating movements.
The pumping apparatus 2 according to the depicted embodiments of the invention additionally comprises a phase shifter 49. Said phase shifter 49 is adapted for varying the phase relationship between the reciprocating motions of the two pistons 13, 14. In principle, the phase relationship between the movements of the pistons 13, 14 can be adjusted to any value. For the purpose of reducing pressure pulsations in the flow of the liquid delivered by the pumping apparatus 2 relatively small adjustments or small shiftings of the phase relationship between the motions of the pistons 13, 14 are effectual. For example, the realisation of phase shifting not exceeding 10% of the stroke period can be sufficient.
In the embodiment depicted in
The auxiliary drive 50 preferably is adapted for inducing enough torque into the second nut 29 such that the second nut 29 can move parallel to the longitudinal extension of the second spindle 26 without any rotary motion. In this case the auxiliary drive 50 is controlled by the controller 8 for introducing enough torque into its shaft 54 such that the shaft 54 stands still and does not rotate when the second spindle drive 24 is in operation and the second spindle 26 rotates in order to move the second nut 29 parallel to the longitudinal extension of the second spindle 26. Since the second nut 29 is torque proof guided parallel to the longitudinal extension of the second spindle 26 by the coupling gear 51 when the phase shifter 49 is deactivated and the auxiliary drive 50 is controlled to hold on its shaft 54, the adjusted phase relationship between the motions of the two pistons 13, 14 is fixed. But as soon as the auxiliary drive 50 induces a rotary motion into the second nut 29 the second nut 29 can be adjusted along the second spindle 26 resulting in an adjustment of the phase relationship between the motions of the two pistons 13, 14. The phase shifter 49 varies the conversion rate of the respective spindle drive 23, 24 in order to provide the respective phase shift.
Since the phase shifter 49 is assigned to the second pump 10 the auxiliary drive 50 is, for example, adapted for inducing a rotary motion into the second nut 29 in order to timely shifting the top dead center of the second piston 14 to a timepoint later in order to vary the phase relationship between the reciprocating motions of the pistons 13, 14. Timely shifting the top dead center of the second piston 14 to a later timepoint results in a predetermined and timely limited transition period in which both pistons 13, 14 can move in the same direction such that the first piston 13 can start its pumping stroke while the second piston 14 is still performing its pumping stroke. Due to this specific phase shifting a drop in pressure in the second chamber 16 due to the reversing of the second piston 14 at its top dead center while the first piston 13 still is in compression phase can be avoided or at least significantly reduced. This is because the timely enlarged pumping stroke of the second piston 14 enables the first piston 13 to build up the demanded high pressure within the first chamber 15 to prepare delivery.
While in the embodiment according to
It should be clear, that the present invention is not restricted to phase shifters 49 comprising an auxiliary drive 50 and a coupling gear 51. Other embodiments of said phase shifter 49 may for example cooperate with a cam which is situated either between the respective housing 17, 18 and the casing (not shown) of the pumps 9, 10 or between the respective front end 45, 46 of the respective piston 13, 14 and the gear 31. For example, it is, in principle, possible to use said cam instead of the ball 38. In order to shift the phase relationship between the two pistons 13, 14, the cam can be rotated with help of an adequate drive to vary the distance between the respective nut 28, 29 and the respective piston 13, 14.
Since the phase shifter 49 according to
In the preferred embodiments according to the
Due to the compressibility of the liquid at the requested high pressure the transition from the suction stroke of the first piston 13 to the pumping stroke of the first piston 13 results in a drop of pressure in the second chamber 16 when the phase relationship between the motions of the pistons 13, 14 is fixed to a value exactly synchronizing the bottom dead center of the first piston 13 to the top dead center of the second piston 14. As a matter of fact the pressure in the second chamber 16, which has a small volume with the second piston 14 at its top dead center, drops faster than the pressure can be built up in the first chamber 15, which has a big volume with the first piston 13 at its bottom dead center. A fixed phase relationship between the motions of the pistons 13, 14 as used in conventional pumping apparatuses results in pressure pulsations at the outlet port 4 of the pumping apparatus 2. The phase shifter 49 is operated to reduce such pressure pulsations.
In the embodiment depicted in
During the following suction stroke of the second piston 14 the phase shifter 49 is operated to reverse the phase shift in order to reestablish the original phase relationship between the two pistons 13, 14. In a preferred embodiment at least at the end of the suction stroke of the second piston 14 the motions of the two pistons are synchronized such that the second piston 14 arrives at its bottom dead center essentially at the same time as the first piston 13 arrives at its top dead center.
Referring to
The controller 8 or the control circuitry 8 of the pumping apparatus 2 may for example be designed as shown in
A pump drive controller 57 is connected to the system controller 55. A main control loop for controlling the movement of the main drive 30 is indicated by block 58, position servo. The actual value for the position of the main drive 30 to be used in the main control loop 58 may be provided from the angular position indicator 72 and the target value is provided from the pump drive controller 57. An auxiliary control loop for controlling the movement of the auxiliary drive 50 is indicated by block 59. The actual value for the position of the auxiliary drive 50 to be used in the auxiliary control loop 59 may be provided from the angular position indicator 60 and the target value is provided from the pump drive controller 57.
Also connected to the system controller 55 may be an inlet controller 61 which controls the opening and the closing of the inlet valve 5 in coordination with the movement of the first piston 13. The control signals are supplied to the solenoid 7 on a line 62.
The pressure of the delivered liquid may be measured by a pressure transducer, which is for example arranged in the damping unit 22. Here the analog output signal of the pressure transducer is supplied on a line 63 to an A/D-converter 64 by which it is converted into a digital signal. This digital signal is supplied to the system controller 55 from which it can be used to control phase shift operation and also passed to the user interface 56 and displayed.
Referring now to the
First blocks indicated by 69 each represent the suction stroke of the first piston 13 and the pumping stroke of the second piston 14. Second blocks indicated by 70 each represent the pumping stroke of the first piston 13 and the suction stroke of the second piston 14. With 71 a transition zone or period is indicated, in which both pistons 13, 14 move in the same direction.
On the left side of each of
If the phase shifter 49 is assigned to the second piston 14 according to the example depicted in
In the example depicted in
Accordingly, the line 67 representing the operation of the auxiliary drive 50 shows sharp falling flanks. Each falling flank is followed by a smoothly increasing flank and each increasing flank is followed by a horizontal portion each followed by another falling flank. During each falling flank the auxiliary drive 50 operates inverse or antiparallel to the operation of the main drive 30 for maintaining the pumping stroke of the second piston 14 and for maintaining the high pressure in the second chamber 16. During each increasing flank the auxiliary drive 50 operates parallel to the operation of the main drive 30 in order to smoothly reestablish the original phase relationship between the two pistons 13, 14. During each horizontal portion the auxiliary drive 50 is operated for providing a torque proof guiding for the second nut 29 such that the second nut 29 is torque proof, i.e. without rotation, moveable parallel to the longitudinal extension of the second spindle 26. During these horizontal portion the phase shifter 49 is deactivated.
The dotted line 68 represents the operation of the main drive 30 during a specific operating mode. This specific operation mode is characterized by a timely limited higher driving power of the main drive 30 resulting in a higher speed of rotation and in the end resulting in a higher velocity of at least the first piston 13 at the beginning of its pumping stroke. Accordingly, said dotted line 68 starts at the bottom dead center of the first piston 13 with a very steep increasing flank for a relatively short time. This steep flank is followed by another increasing flank having a smaller gradient. For example, during the steep flank main drive 30 operates with a driving power level resulting in a velocity of the first piston 13 being ten times higher than the velocity of the first piston 13 during the following flank having the smaller incline. This specific operation mode reduces the time necessary for building up the high pressure in the first chamber 15. Accordingly, said specific operation mode reduces pressure pulsations in the liquid delivered by the pumping apparatus 2. It is clear, that this specific operation mode can be performed additionally to the phase shifting realized by the phase shifter 49 as described above. Also it should be clear, that the above mentioned reduction of stroke lengths depending on the liquid mass flow to be delivered can be performed additionally or alternatively to said specific operation mode together with the phase shifting according to embodiments of the present invention.
In the example depicted in
Due to this operation of the phase shifter 49 the first piston 13 arrives at its bottom dead center timely before the second piston 14 arrives at its top dead center. The beginning of the transition zone 71 is designed such that the first piston 13 has enough time to build up the requested high pressure in the first chamber 15 until the transition zone 71 ends by the second piston 14 arriving at its top dead center.
During the rest of this pumping stroke 70 of the first piston 13 the phase shifter 49 is operated to reestablish the original phase relationship between the two pistons 13, 14.
The operation of the phase shifter 49 can be derived from the line 67 representing the operation of the auxiliary drive 50. During the transition period 71 the line 67 shows a steeply increasing flank beginning and ending together with the transition period 71. Each inclining flank may be followed by a smoothly falling flank that preferably ends together with the pumping stroke 70 of the first piston 13. Each falling flank may be followed by a horizontal portion of the line 67 extending along the respective suction stroke 69 of the first piston 13. During the inclining flank the auxiliary drive 50 operates antiparallel or inverse to the main drive 30 such that the first piston 13 passes through its bottom dead center and starts building up the high pressure in the first chamber 15 although the main drive 30 is still operated to force the second piston 14 in its pumping (delivering) direction. Accordingly, during the transition zone 71 both pistons 13, 14 move in the same direction, namely in their pumping (delivering) direction. During the falling flank the phase shifter 49 is operated to reestablish the original phase relationship between the two pistons 13, 14. Accordingly, the auxiliary drive 50 operates parallel to the operation of the main drive 30 preferably for the rest of the remaining pumping stroke of the first piston 13. At least at the end of the pumping stroke 70 of the first piston 13 the original phase relationship between the motions of the pistons 13, 14 is reestablished.
The position and in particular the length of the transition period 71 can be determined empirically and stored in an adequate map or characteristic diagram as a function of pressure. Major factors are physical properties of the liquid pumped (mainly compressibility) in combination with technical parameters (mainly elasticity and deadcolume of the pump chamber 15 when the first piston 14 is in its upper dead center position) of the pump setup in use. These parameters can be determined empirically as individual values and stored in adequate maps or characteristic diagrams, preferably all as a function of pressure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 06122912.6 | Oct 2006 | EP | regional |
