WO1995026469A1

WO1995026469A1 - Pulsation-poor reciprocating piston pump

Info

Publication number: WO1995026469A1
Application number: PCT/EP1995/001093
Authority: WO
Inventors: Peter Lamp
Original assignee: Mediador Pumpentechnik Gmbh
Priority date: 1994-03-29
Filing date: 1995-03-23
Publication date: 1995-10-05
Also published as: DE4410910A1; DE4410910C2

Abstract

A reciprocating piston pump for a fluid has at least one pair of cylinders (12, 13) whose pistons (14, 15) may be continuously driven by a drive shaft (29), in particular a motor-driven shaft. In order to make possible a practically pulsation-free operation, the connections of the rods (30, 31) of the pistons (14, 15) are mutually offset by 90° at the drive shaft (29) and the control cams of both piston rods (30, 31) are guided in such a way along their path that the total volume flow of fluid displaced from the chambers (12a, 13a) of both cylinders (12, 13) is constant in time.

Description

Low pulsation piston pump

The invention relates to a reciprocating piston pump for a fluid with at least one pair of cylinders, the pistons of which can be driven continuously by a transmission shaft, which can be driven in particular by a motor, the connections of the piston rods belonging to the pistons being offset from one another by an angle of 90 ° on the transmission shaft. Such a reciprocating pump is known from DE 32 03 722 AI.

Furthermore, the invention relates to a reciprocating piston pump for a fluid with at least one pair of cylinders, the pistons of which can be driven continuously by independent electrical drives forming a frequency-controlled transmission, the piston rods belonging to the pistons being driven at an angle of 90 ° to one another.

Reciprocating piston pumps have the disadvantage that they usually convey the medium (fluid) to be pumped in an uneven flow, which causes pressure surges which are caused by the pulsation of the fluid. Particularly in the case of such reciprocating piston pumps which are driven by a rotary drive via a crank mechanism, considerable differences in the flow velocities and shocks occur during operation when the Piston reverses its direction of movement. These pressure surges must be mitigated by compensators in the lines, or wind boilers are used on the suction side and pressure side, which should equalize the flow rate. As a result, the pump takes up a large amount of space and is complex in its construction. Other known pumps use compensating pumps or pilot control devices.

Single-acting three-cylinder pumps are known in order to keep the fluctuations in the delivered liquid volume as low as possible (e.g. German patent 430610). With this combination, the pulsation can be reduced, but not completely switched off.

From DE-OS 24 46 805 a metering pump is known, the two oppositely oscillating pistons are each operatively connected to one of two cams offset by 180 °, the cam curve being designed such that the positive region of each cam curve is used to achieve a pulsation-free flow rate is divided into a work area and a pre-compression area. The working area of the cam curve of both cams is designed such that the sum of the piston speeds in the displacement direction is constant, while the pre-compression area is designed such that the piston has reached its working pressure position when the cam is at the transition between the pre-compression area and the working area. In this way it is ensured that at the transition of the pumping from one pump head to the other there is no drop in the volume flow, because at this moment the piston starting to work has already reached a position in which to work with the working pressure due to the precompression area of the cam curve begins. However, such a pump has the Disadvantage that it is not fully speed-regulating due to the suction generated by springs.

The invention has for its object to design a reciprocating pump so that a constant total volume flow of the fluid can be achieved with reasonable technical effort.

According to the invention, this object is achieved in a first variant in that the cam control of the respective piston rod takes place via a cam disk in which a guideway for the piston rods is dimensioned such that the piston stroke (X) and angle of rotation on the crank disk (Y) relative to one another according to the equation

X = H C

are related, where C is a constant, and wherein the cam controls of the two piston rods take place along their respective trajectory such that the total volume flow of the fluid displaced by the cylinder spaces of the cylinder pair is constant over time.

The solution according to the invention is characterized in that the 90 ° displacement of the piston rods on the one hand and the cam control of the two piston rods with a view to achieving a constant total volume flow on the other hand creates a pulsation-free device. As a result, compensators, pilot control devices or wind boilers are not required. In addition, it is possible to use fluids whose viscosity changes significantly depending on the temperature Pumping speed. The constancy of the total volume flow of the fluid results from the fact that the piston of one cylinder has its maximum speed just at the time when the other piston has reached its top or bottom dead center. At the same time, the acceleration of the first piston in one cylinder is offset by a correspondingly large deceleration of the piston in the other cylinder, so that the sum of the volume flow delivered in both cylinders remains the same for the same volumes. The usable volumes of the cylinder chambers of both cylinders are dimensioned such that the first and second pistons displace the same volume of the medium to be pumped with each stroke.

By fulfilling the arithmetic condition

X = c

the pump works according to a displacement function, according to which the sum of the piston strokes is superimposed in such a way that the total volume flow is constant over time.

A particularly preferred embodiment of the invention provides that valves are provided in the supply lines and discharge lines for controlling the inflow and outflow of the fluid to the cylinder spaces, the material density of the valve body of the valves approximately corresponding to the density of the fluid. Such a valve arrangement enables an inertia-free valve function, which is particularly important in connection with the reciprocating pump control according to the invention. In that the accelerating masses of the valve body are adapted to those of the fluid to be pumped, there is no inertia-related vibration or

Lag effects. Rather, the valve body tracks the movement of the fluid without delay.

Further preferred embodiments are presented in the following subclaims.

According to a second variant of the invention, the above-mentioned object is achieved in that the respective piston rods are driven in such a way that the piston stroke and angle of rotation relative to one another according to the equation

X

C

are related, where C is a constant, and wherein the control of the piston rods is carried out such that the total volume flow of the fluid displaced by the cylinder space of the cylinder pair is constant over time.

This variant is characterized in that a frequency-controlled electrical gear unit acts instead of the gear shaft, via which the piston rods are controlled. Each of the piston rods is controlled by an associated electric motor. This variant has the same advantages mentioned above, but is characterized by a simpler mechanical structure.

The invention is explained in more detail below on the basis of exemplary embodiments. Show:

1 shows a first embodiment of the reciprocating piston pump according to the invention in schematic cross section,

2 shows a section through the cam plate for controlling the piston rod,

Fig. 3 is a representation of the displacement function, according to which the reciprocating pump according to the invention works and

Fig. 4 is a detailed drawing that shows the detail of the pump in the region of a valve 25.

Fig. 5 shows a second embodiment of the invention in cross section.

In the pump housing 11 of a reciprocating piston pump 10, a first cylinder bore 12 and a second cylinder bore 13 are arranged parallel to one another at a lateral distance from one another. The first cylinder 12 is divided by a first, double-acting piston 14 into an upper cylinder chamber 12a and a lower cylinder chamber 12b. In the same way, a second double-acting piston 15 also divides the second cylinder 13 into an upper cylinder chamber 13a and a lower cylinder chamber 13b. A feed line 16, 17, 18, 19 opens into each cylinder chamber 12a and 12b or 13a and 13b, and a discharge line 20, 21, 22, 23 for the medium (fluid) to be pumped is connected to each cylinder chamber.

In all supply and discharge lines, automatic spring-loaded valves 24 and 25 are arranged, of which the valves open in the supply lines 16-19, if, in the cylinder chambers to which the respective supply lines are connected, a vacuum occurs during the suction stroke of the piston and from which the valves 25 in the lines 20-23 open when the pistons 14 and 15 exert a pressure stroke.

All supply lines are connected to a common collective supply line 26, while all of the pumps' discharge lines are connected to a common collective lead, not shown here, which leads to a consumer (not shown).

The pump 10 is driven by a controllable electric motor 27 via a crank mechanism 28, to the triple-bearing crankshaft 29 of which the connecting rods 30 for the first piston 14 and 31 for the second piston 15 are connected. The push rods 30 and 31 are connected via slide tracks 32 and 33 to the piston rods 34 and 35 of the first piston 14 and the second piston 15, which are guided in slide guides 36 and are sealed with the stuffing boxes 37 with respect to the pump housing 11.

The connection 38 of the cam pin 39 of the push rod 35 for the second piston 15 is offset on the crankshaft 29 relative to the connection 40 of the cam pin 41 of the push rod 30 for the first piston 14 by an angle of 90 °, so that the second piston 15 is exactly is in the middle of the cylinder 13 when the first piston 14 reaches its bottom or top dead center. In the drawing, that position is shown in which the first piston 14 is at its bottom dead center and has ended the pressure stroke in the lower chamber and the suction stroke in the upper chamber, while the second piston 15 with its maximum piston speed the pressure stroke for the lower Cylinder chamber 13b and the suction stroke for the upper cylinder chamber 13a.

When the crankshaft 29 continues to rotate in the direction of the arrow 42 in the Y direction shown, the second piston 15 initially continues its stroke in the same direction (the X direction shown), the piston speed becoming slower towards bottom dead center while the first piston reverses its direction of movement and draws the fluid to be conveyed through the feed line 16 into the lower cylinder space 12b and compresses the fluid located in the upper cylinder space 12a and ejects it through the discharge line 21, the valve 25 in the discharge line 21 being opened and the valve 24 is closed in the feed line 17.

As the speed of the second piston 15 decreases, the speed of the first piston 14 increases, so that the sum of the volume flows VI and V2 of the medium conveyed by both pistons 14 and 15 is constant.

To achieve this, the volumes of the cylinder chamber 12a, 12b, 13a, 13b of both cylinders 12 and 13 must be dimensioned and matched to one another such that both pistons 14 and 15 displace equal volumes of the medium to be pumped with each stroke, which is simple can be achieved in that the shape and dimensions of both cylinders and pistons in the individual cylinder spaces are the same or are balanced by a predeterminable factor in the cam track.

Fig. 2 shows a detail from which the control of the push rods 30 and 31 can be seen by means of a cam plate 43. The cam plate 43 has a circular circumference, but is eccentric on the Crankshaft 29 attached. It is attached using a feather key. The cam plate 43 has a guide track 44 for the push rod 30 or 31, which is incorporated as a recess.

The course of the guideway results from a calculation such that piston stroke X and angle of rotation Y (measured in rad) of crankshaft 29 satisfy the following equation:

X = IL C

where the constant C is determined according to predetermined dimensions.

The guideway can be milled into the cam plate 43 based on its calculation derived from the formula.

As can be seen from the equation corresponding displacement function according to FIG. 3, it is fulfilled for each angle (Y direction) that the volume flows in the two cylinders 12, 13 each overlap to form a constant total volume flow.

4 shows a detail of the reciprocating piston pump according to the invention in the region of the valves 24 and 25.

A valve 25 consists of a valve body 25a, which is acted upon by a compression spring 25b against the valve seat 25c. The opening length of the valve 25 is limited by the stop 25d. The valve body 25a consists of Teflon, which has a low specific weight, the value of which corresponds approximately to that of the fluid to be pumped and is compatible with the fluid.

This design leads to the fact that each valve follows the fluid to be displaced practically without inertia, without there being superimposed pulsations.

The second exemplary embodiment of the invention shown in FIG. 5 differs from that which was shown in FIG. 1 or was previously explained essentially only in that the cam mechanism 28 is formed from a disk, one end face of which is a first guide track 44 for the one push rod 30 and the other end face has a guide track 44 for the other push rod 31. The design of the guideways is dimensioned as previously described. The disk is mounted in the pump housing (dashed line) and is driven by a gear 45, which is set in rotation by the electric motor 27. The speed ratios can be adjusted accordingly by dimensioning the gearwheels of the gearbox 45 accordingly.

The main feature of this pump is that it enables an extremely slim design to be achieved and that the disk itself can be used as a gearbox.

In a variant of the invention as an alternative to the embodiment shown in FIG. 1, it can be provided that the unit consisting of the crankshaft and cam disks can be dispensed with, and instead the piston rods 30, 31 of the pistons 14, 15 can be operated directly by electric motors. The electric motors are controlled in such a way that the piston rods 30, 31 on the one hand are moved at 90 ° to one another and, on the other hand, the characteristic of the control is such that the above-mentioned equation

X =

is fulfilled at all times. This condition can be met in that the electric motors form a frequency-controlled transmission unit in which a corresponding control program for the piston rods is stored. This is a technical equivalent to the embodiment of the invention shown in FIG. 1.

Claims

PATENT CLAIMS

1. Reciprocating piston pump for a fluid with at least one pair of cylinders (12, 13), the pistons (14, 15) of which can be driven continuously by a crankshaft (29), which can be driven in particular by a motor, the connections of the piston rods belonging to the pistons (14, 15) (30, 31) are offset from one another by an angle of 90 ° on the gear shaft (29), characterized in that the cam control of the respective piston rod (30, 31) takes place via a cam disk in which a guide track for the piston rods (30, 31) is dimensioned such that the piston stroke (X) and angle of rotation on the crank disk (Y) to one another according to the equation

X =

in which C is a constant and the curve controls of the two piston rods (30, 31) take place along their respective trajectory such that the total volume flow of the fluid displaced by the cylinder spaces (12a, 13a) of the pair of cylinders (12, 13) is constant over time.

2. Reciprocating piston pump according to one of the preceding claims, that the guide track is arranged eccentrically on the crank disk.

3. Reciprocating piston pump according to one of the preceding claims, characterized in that for controlling the inflow and outflow of the fluid to the cylinder spaces (12a, 12b, 13a, 13b) valves (24, 25) in the feed lines (16 - 19) and discharge lines ( 20 - 23) are provided, which are adapted to the kinematic mass of the fluid.

4. Reciprocating piston pump according to claim 3, that the material density of the valve body of the valves (24, 25) approximately corresponds to the density of the fluid.

5. Reciprocating piston pump according to claim 4, that the valve body material is a plastic, in particular Teflon.

6. Reciprocating piston pump according to one of the preceding claims, characterized in that all feed lines (16 - 19) to the cylinder spaces (12a, 12b, 13a, 13b) have a common collecting line (26) and all discharge lines (20 - 23) from the cylinder spaces (12a , 12b, 13a, 13b) are connected to a common collector.

7. Reciprocating pump according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the drive is a controllable motor (27).

8. Reciprocating piston pump according to one of the preceding claims, that a plurality of cylinders, the pistons of which are all connected to a common transmission shaft, are provided.

9. Reciprocating piston pump for a fluid with at least one pair of cylinders, the pistons (14, 15) of which can be driven continuously by independent electric drives forming a frequency-controlled transmission, the piston rods belonging to the pistons (14, 15)

(30,31) are driven at 90 ° to each other, that is, that the

The respective piston rods (30, 31) are driven in such a way that the piston stroke (X) and angle of rotation (Y) to one another according to the equation

X = left c

in which C is a constant, and the control of the piston rods takes place in such a way that the total volume flow of the fluid displaced by the cylinder spaces (12a, 13a) of the cylinder pair (12, 13) is constant over time.