EP0314994B1 - Pump arrangement with double pump - Google Patents

Abstract

A pump arrangement (1) has two alternately conveying separate pumps (2, 3) and one axial piston motor (14). The piston rod (19) of the latter is divided into two sections (20, 21) each assigned to a separate pump (2, 3). Their spacing is variable by means of an adjusting device (22). Each section (20, 21) is connected to an actuating element (39, 40), each of which is assigned to one of the two limit position switch elements (37, 38) and actuates this at the end of each motor stroke. The axial piston motor (14) has two pistons (6, 11), each connected to a piston rod section (20, 21), which pistons are located in the area of an end surface (41, 42) of the piston displacement (15, 16) when the associated limit position switch element (37, 38) is actuated. If a minimum of two double pumps are used, a pump arrangement is created for two-component or multiple- component operation in which the component pumps are steplessly lift- adjustable, do not have to perform any dead travel and thereby work with low pulsation. <IMAGE>

Description

The invention relates to a pump arrangement with a double pump, which has two alternatingly delivering individual pumps, in which a piston valve provided with a reversing valve, in particular a pneumatic piston motor, drives the individual pumps by means of its reciprocating piston rod. the piston rod is connected to actuating elements which are each assigned to one of the two limit switch elements and actuate this in each case at the end of the motor stroke corresponding to the suction stroke of the associated individual pump and the piston engine has two pistons connected to the piston rod, the stroke volume of which is adjustable.

The term "piston" is used here in its general meaning. It includes all forms of engine elements that axially drive the piston rod when pressurized. This includes not only rigid pistons that can be slid in the cylinder, but also pistons designed as a membrane or combined with them.

In a known pump arrangement of this type (US-A-43 81 180) two approximately parallel membranes are provided, each of which separates a pump chamber and an engine compartment, the engine compartments being on the mutually facing sides of the membranes. The diaphragms are connected by a one-piece, continuous piston rod on which the actuating elements can be changed the effective pump stroke are adjustable. However, each adjustment also leads to a change in the size of the displacement of the pneumatically operated motor at the beginning of the pressure stroke. Accordingly, pressure build-up times vary in length. The delivery strokes of the two individual pumps can be spaced a considerable distance apart, which results in disturbing pulsations.

In a further known pump arrangement (DE-OS 30 31 067), a pneumatic axial piston motor is arranged between the two individual pumps. The end position valves are arranged on the end walls of the engine cylinder and are actuated by the piston just before it touches the front wall. The two limit switch elements designed as valves in turn control the reversing valve. The pneumatic axial piston motor therefore has a constant stroke. For each individual pump, the piston rod carries along a displacement piston which is guided in a cylinder and which, during each pressure stroke, conveys pressure fluid from its displacement into a working space delimited by an axially movable pump element, namely a membrane. Here, a liquid container is provided, which is connected to the displacement at least at the end of the suction stroke by means of a valve. The valve is formed in that the end face of the displacer covers a control opening in the cylinder wall. To change the pump stroke volume, the cylinders and thus the control openings can be moved axially using a rotary knob. As a result of this shift, the dead travel changes until the control opening is covered and thus the effective stroke volume. The adjustment must be made separately for each individual pump. It is difficult to make the same volume change for both pumps.

In another known pump arrangement (DE-OS 35 44 016), a pneumatic axial piston motor with a constant stroke actuates two double pumps, the actuating rods of which can be taken from the motor piston rod via a coupling piece. The actuating rod of a double pump consists of two sections which are connected to one another via a clamping device, so that the axial distance between the two rod sections is changed symmetrically to one another by turning the clamping sleeve. As a result, the dead travel that each displacement piston has to travel through until the control opening in the housing-fixed cylinder is overridden, which leads to an equally large change in the stroke volume in both individual pumps leads. If the stroke volume is adjusted to lower values, the drive power is periodically fluctuating unevenly distributed among the pumps working in parallel.

The invention is based on the object of specifying a pump arrangement of the type described at the outset which is suitable in particular for the conveyance of two or more components and with stepless stroke adjustment, in which the pulsation can be kept lower.

This object is achieved according to the invention in that the piston rod has two sections which are assigned to a single pump and are designed as parts and are firmly connected to the respective pistons and the actuating elements, the axial spacing of the sections being changeable by means of an adjusting device, and in that the Piston when actuating the associated limit switch element for each stroke volume set by the adjusting device is in contact with an end face of the engine displacement or somewhat in front of it.

With this design, the respective stroke volume of the two individual pumps is determined by the stroke of the axial piston motor. While the pistons of the motor and the pump elements of the individual pumps assume reversing positions at the end of the pressure stroke, which are dependent on the stroke setting, they reach the same end position with each stroke setting at the end of the suction stroke. Therefore, the volume of the engine displacement to be filled with pressure medium, in particular compressed air, up to the beginning of the pressure stroke of the respective individual pump is constant regardless of the stroke setting and can be achieved by appropriate design of the dead space be kept to a minimum. This results in a favorable efficiency. Since the individual pumps do not have to travel through dead paths, their pressure strokes can be connected directly to one another, so that a pressure drop caused by an idle stroke is avoided. The pump arrangement is therefore particularly suitable for the continuous supply of spray devices.

There are various options for axial adjustment. A symmetrical adjustment is preferred. This is achieved in a simple manner in that the adjusting device has a coupling piece which engages with opposing threads on the two piston rod sections and is provided with a torque engagement surface.

It is particularly advantageous that the pistons are supported in their end position on the end face of the engine displacement. As a result, the dead space in the engine displacement can be kept particularly small. In addition, the limit switch element is protected against overload.

In a preferred embodiment, the two pistons of the axial piston motor each delimit an engine displacement with their sides facing one another and each with a space under ambient pressure with their sides facing away from one another.

In an alternative, the two pistons of the axial piston motor each limit an engine displacement with their sides facing one another and a pump chamber of an individual pump with their sides facing away from each other.

If the piston rod carries a displacement piston in a cylinder for each individual pump, which conveys pressure fluid from its displacement into a working space delimited by an axially movable pump element for each pressure stroke, and a liquid container is provided which is connected to the displacement by means of a valve at least at the end of the suction stroke is connected, one can arrange the cylinders for both displacement pistons fixed to the housing due to the end position of the displacement pistons which is independent of the stroke setting.

In this context, it is advantageous that the displacer guided in the cylinder bore is axially displaceable relative to the piston rod by a limited amount, that the drive of the displacer during the pressure stroke by contacting an end face of the piston rod on the end face of the displacer facing away from the displacement and the drive during the suction stroke by means of two oppositely directed driving surfaces on the piston rod and displacement piston, and that the valve is formed between the end faces of the piston rod and displacement piston lying against one another during the pressure stroke and is connected to the displacement space via at least one longitudinal channel running through the displacement piston. With this further training, a compensation in the case of a lack of liquid in the work space is possible. This reduces leakage losses and the associated disadvantages.

A particularly useful application of the invention is the promotion of two or more components. This is done by at least one second, two alternately delivering single pumps having double pump, the axial piston motor runs through a stroke determined by stationary limit switch elements, and by a reversing valve circuit that operates the double pumps in the same or push-pull mode. In this way, with mix two or more components with high accuracy. A preferred application is the supply of two-component paints to a spraying device.

Here, the second double pump can have a fixed stroke or also an adjustable stroke. Any mixing ratio can be set in a wide range. The synchronous reversal ensures that each stroke of one double pump corresponds to one stroke of the other double pump.

A common start of stroke can be achieved in a very simple manner in that two series connections, each with a limit switch element of each double pump, are provided for reversing the double pumps. The reversal of the double pumps only takes place when both or all double pumps have reached their end position.

Furthermore, a common reversing valve can be provided for at least two double pumps. This simplifies the structure.

Three or more double pumps can also be provided and their limit switch elements connected in series.

Fig. 1

einen Längsschnitt durch eine erfindungsgemäße Niederdruck-Pumpenanordnung,

Fig. 2

schematisch die Pumpenanordnung der Fig. 1 mit einem Schaltbild,

Fig. 3

einen Teillängsschnitt durch eine erfindungsgemäße Hochdruck-Pumpenanordnung,

Fig. 4

einen Teillängsschnitt durch eine dritte Ausführungsform und

Fig. 5

zwei Doppelpumpen mit zugehörigem Schaltbild.

The invention is explained in more detail below in the drawing of preferred exemplary embodiments. Show it:

Fig. 1

2 shows a longitudinal section through a low-pressure pump arrangement according to the invention,

Fig. 2

1 shows schematically the pump arrangement of FIG. 1 with a circuit diagram,

Fig. 3

2 shows a partial longitudinal section through a high-pressure pump arrangement according to the invention,

Fig. 4

a partial longitudinal section through a third embodiment and

Fig. 5

two double pumps with associated circuit diagram.

The double pump 1 illustrated in FIG. 1 comprises two single pumps 2 and 3. The single pump 2 has a pump chamber 4 which is delimited on the one hand by an end wall 5 and on the other hand by a piston 6 designed as a membrane. The pump chamber 4 is connected to a suction line via a suction valve 7 and to a pressure line via a pressure valve 8. In the same way, the individual pump 3 has a pump chamber 9 which is delimited by an end wall 10 and a piston 11 designed as a membrane. The pump chamber 9 is also connected to a suction valve 12 and a pressure valve 13.

The two individual pumps 2 and 3 are driven with the aid of an axial piston motor 14, which has two engine displacements 15 and 16, which are limited on the one hand by a housing wall 17 and 18 and on the other hand by the pistons 6 and 11, which act here as engine pistons .

The two pistons 6 and 11 are connected via a piston rod 19 which has a first section 20 which is connected to the piston 6 and a second section 21 which is connected to the piston 11. The two sections are connected to one another by an adjusting device 22 in the form of a coupling piece which engages with two opposing threads 23 and 24 in the two piston sections 20 and 21 and with a torque engagement surface 25 is provided. After loosening two lock nuts 26 and 27, the axial distance between the two sections 20 and 21 can be changed.

A reversing valve 28 designed as a 5/2-way valve has a flat slide 29 which connects a compressed air inlet 30 optionally via a duct 31 to the engine displacement 15 or via a duct 32 to the engine displacement 16. The respective other engine displacement is connected to the ambient air via the interior of this reversing valve 28 and an outlet 33. The flat slide 29 is displaced by an actuating slide 34 when the one of the two control pressure spaces 35 and 36 on the front side is supplied with compressed air.

Two fixed end position valves 37 and 38 are provided as end position switching elements. An actuating element 39 for the end position valve 37 is firmly connected to the piston rod section 21, an actuating element 40 for the end position switching valve 38 is firmly connected to the piston rod section 20. The position of the actuating elements 39 and 40 is such that, shortly after actuation of the end position valves, the associated piston 11 on an end face 41 or the piston 6 on an end face 42 of the respective engine displacement 15 or 16 for abutment or somewhat in front of it to hold can come.

2, the double pump 1 with the two single pumps 2 and 3 and the two-part motor 14 is illustrated schematically. The two end position valves 37 and 38 are connected via control lines L1 and L2 to the control pressure chambers 35 and 36 of the reversing valve 28. The inlet 44 feeds the two end position valves 37 and 38 with compressed air. The axial piston motor 14 goes back and forth continuously, each pump 2 and 3 alternately delivering the same stroke volume.

By adjusting the adjusting device 22, the distance between the two pistons 6 and 11 can be changed. As a result, the distance between the actuating elements 39 and 40 is changed at the same time. This leads to a variation in the engine and pump stroke, but the position of the pistons remains unchanged at the end of the suction stroke.

In the embodiment according to FIG. 3, reference numerals raised by 100 are used for corresponding parts.

The first difference is that the axial piston motor has two rigid pistons 106 and 111. They limit the engine displacement 115 and 116 on the sides facing each other. The spaces 146 and 147 delimited by the opposite piston sides are connected to the atmosphere via channels 148 and 148 '.

The single pump 102 has a pump chamber which is delimited by a pump element 149 in the form of a membrane. This rests under the influence of a return spring 150 against a support plate 152 provided with holes 151. When a displacement piston 153 is pushed to the left by the piston rod 119 in the cylinder 154 fixed to the housing, pressure fluid is displaced from the displacement 155 into a working space 156 between the support plate 152 and the pump element 149. During the suction stroke of the displacement piston 153, the pump element 149 returns under the influence of the return spring 150 back to the illustrated resting position.

The displacer piston 153 has a circumferential seal 163 and an inner channel 157. In the rest position, it is supported by a spring 158 with its seal End face 159 pressed against an end face 160 of the piston rod 119. There are stops 161 outside the piston rod. Therefore, when the piston rod 119 is pulled back further, a valve opens, which is formed between the end face 159 and the end face 160. Liquid can then flow from a liquid container 162 into the displacement 155 if this is necessary. During the pressure stroke, the piston rod 119 takes the displacer piston along by abutting the end faces 159 and 160. During the suction stroke, in which lower forces are required, the spring 158 is sufficient between two opposing driving surfaces in order to return the displacement piston 153. Further details can be found in DE-OS 35 42 926. Also in this context, it is of interest that the piston rod always assumes the same end position regardless of any stroke volume adjustment, in which the valve between the end faces 159 and 160 is just slightly open is.

The double pump 101 is constructed symmetrically. The parts of the second individual pump correspond to those of the first individual pump 102.

For the embodiment according to FIG. 4, reference numerals increased by 200 are used for corresponding parts. Only the single pump 202 of the double pump 201 is illustrated. The section 220 of the piston rod 219 is firmly connected to a displacement piston 253, which is guided in the cylinder 254 fixed to the housing with the interposition of a seal 263. The displacement piston 253 therefore acts as a pump element directly in the pump chamber 204.

5, two double pumps 101 and 101a are schematically illustrated. The double pump 101 has the single pumps 102 and 103, which are of the two-part axial piston motor 144 are driven. The double pump 101a has the single pumps 102a and 103a, which are driven by the two-part axial piston motor 114a. A reversing valve 128 is common to both double pumps. The channel 131 therefore leads to one engine cubic capacity each and the channel 132 likewise leads to one engine cubic capacity each of the two double pumps 101 and 101a.

The end position valve 137 supplied with compressed air at the inlet 144 is connected in series with the end position valve 137a and only this series connection acts on one control pressure chamber of the reversing valve 128. In the same way, the end position valves 138 and 138a which are in series with one another are connected to the other control pressure chamber of the reversing valve 128 connected. The consequence of this is that the switchover of both double pumps only takes place when the slower of the two single pumps working in parallel or the single pump covering the larger stroke has reached its end position. Then the changeover takes place, so that a common stroke of both double pumps then takes place again. The series circuits therefore form a reversing valve circuit S in conjunction with the reversing valve 128 designed as a 5/2-way valve, which operates both double pumps in the same or push-pull mode.

5 can be extended to more than two double pumps, in which case the series connections each contain an end position valve of all double pumps. If each double pump is equipped with its own reversing valve, the series connection of FIG. 5 can still be used, in which case a series connection in each case acts on the similar control pressure spaces of both reversing valves. Instead of the end position valves, electrical ones can also be used as end position switching elements Limit switches are used, for example, when the reversing valves are actuated electromagnetically. The series connection can then also be constructed electrically.

Claims (11)

1. Pump arrangement with a double pump having two alternately conveying single pumps, in which double pump a piston motor, in particular a pneumatic piston motor, provided with a reversing valve drives the single pumps by means of its piston rod travelling forwards and backwards, two end position control elements arranged in a fixed position can be actuated at each end of the motor stroke, the piston rod is connected to actuating elements each of which is assigned to one of the two end position control elements and actuates it in each case at the end of the motor stroke corresponding to the intake stroke of the associated single pump, and the piston motor has two pistons connected to the piston rod, it being possible to adjust the stroke volume of the two pistons, characterised in that the piston rod (19; 119; 219) has two sections which are designed as parts (20, 21; 120, 121; 220), each assigned to one single pump (2, 3; 102; 202), and which are rigidly connected to the particular piston (6, 11; 106, 111) and the actuating elements (39, 40; 139, 140), it being possible to alter the axial distance between the sections (20, 21; 120, 121; 220, 221) by means of an adjusting device (22; 122), and in that the pistons (6, 11; 106, 111) are situated resting against a front side end face (41, 42; 141, 142) of the motor stoke chamber (15, 16; 115, 116) or slightly in front of it when actuating the associated end position control element (37, 38; 137, 138) for each stroke volume set by means of the adjusting device (22; 122).

2. Pump arrangement according to claim 1, characterised in that the adjusting device (22) has a coupling piece which engages the two piston rod sections (20, 21) with opposing threads (23, 24) and is provided with a torque working surface (25).

3. Pump arrangement according to claim 1 or 2, characterised in that the pistons (6, 11; 106, 111) are supported in their end position at the front side end face (41, 42; 141, 142) of the motor stroke chamber (15, 16; 115, 116).

4. Pump arrangement according to one of claims 1 to 3, characterised in that the sides of the two pistons (106, 111) of the axial piston motor (114) facing one another each define a motor stroke chamber (115, 116) and the sides facing away from one another each define a chamber (146, 147) under ambient pressure.

5. Pump arrangement according to one of claims 1 to 3, characterised in that the sides of the two pistons (6, 11) of the axial piston motor (14) facing one another each define a motor stroke chamber (15, 16) and the sides facing away from one another each define a pump chamber (4, 9) of a single pump.

6. Pump arrangement according to one of claims 1 to 4, in which for each single pump the piston rod drives a displacement piston in a cylinder which conveys pressure fluid from its stroke chamber to a working chamber, defined by an axially movable pump element, during each pressure stroke, and a fluid container is provided, which is connected to the stroke chamber by means of a valve at least at the end of the intake stroke, characterised in that the cylinders (154) for both displacement pistons (153) are arranged to be fixed to the housing.

7. Pump arrangement according to claim 6, characterised in that the displacement piston (153) guided and sealed in the cylinder bore can be moved axially along a limited length relative to the piston rod (119), in that the displacement piston is driven during the pressure stroke by resting a front face (160) of the piston rod against the front face (159) of the displacement piston facing away from the stroke chamber (155), and is driven during the intake stroke by means of two opposing driving surfaces at piston rod and displacement piston, and in that the valve is formed between the front faces (159, 160) of piston rod and displacement piston lying next to one another during the pressure stroke, and is connected to the stroke chamber (155) by means of at least one longitudinal channel (157) extending through the displacement piston.

8. Pump arrangement according to one of claims 1 to 7, characterised by at least one second double pump (101a) having two alternately conveying single pumps (102a, 103a), the axial piston motor (114a) of this double pump passing through a stroke determined by fixed end position control elements, and by means of a reversing valve connection (S) which operates the double pumps (101, 101a) in phase or out of phase.

9. Pump arrangement according to claim 8, characterised in that two series connections each from an end position control element (137, 137a, 138, 138a) are provided for each double pump to reverse the double pumps (101, 101a).

10. Pump arrangement according to claim 8 or 9, characterised in that one common reversing valve (128) is provided for at least two double pumps (101, 101a).

11. Pump arrangement according to claim 9 or 10, characterised in that three or more double pumps are provided and their end position control elements are connected in series.

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