Note: Descriptions are shown in the official language in which they were submitted.
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DRIVE DEVICE FOR OSCILLATING POSITIVE-DISPLACEMENT MACHINES
The present invention concerns a drive mechanism for oscillating
positive-displacement machines such as for example diaphragm pumps
comprising an eccentric shaft and a plurality of piston rods, wherein the
piston rods are connected to the eccentric shaft in such a way that rotation
of the eccentric shaft produces an oscillating linear movement of the piston
rods.
Oscillatingly operating machines are usually constructed on the basis
of the principle of the straight-thrust crank drive. At high levels of power
or to keep down the oscillating mass forces acting on the machine
foundation, such machines are usually in the form of a multi-crank drive
mechanism. In that case the individual eccentrics with connecting and
piston rods are arranged in mutually juxtaposed relationship either in an in-
line or opposed boxer or radial star form and are driven by a common
crank shaft, the eccentrics of which are respectively displaced relative to
each other by the same angle.
The disadvantage of that structure is essentially that:
- the crank shaft equipped with a plurality of mutually juxtaposed
eccentrics is exposed to high bending moments and has to be of a
correspondingly sturdy dimension,
- particularly in the in-line structure which is the majority of cases
high forces occur in the bearings between the crank shaft and the crank
casing, which pushes up the costs for the bearing,
- complete mass balancing is only possible in the case of a six-
cylinder machine, and
- the drive mechanism overall is of a large structural volume, high in
weight and involves high manufacturing costs.
To overcome those disadvantages multi-cylinder machines have
already been developed in which the piston rods all lie in one plane and are
displaced relative to each other through equal angles. The piston rods are
driven by a single eccentric so that the crank shaft can be of
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correspondingly smaller dimensions. That construction principle is afforded
in two different designs:
a) constructions with a force-locking connection between the
eccentric and the piston rods, in respect of which the piston rods are
pressed against the slide surfaces of the eccentric by return springs, and
b) constructions with a positively locking connection between the
eccentric and the piston rods, in respect of which the return springs are
replaced by a return brace embracing all piston rods.
Both design configurations suffer from disadvantages. Thus when
using a return spring the force thereof is added to the rod force and leads
to an additional loading on the components. If the spring is of excessively
weak dimensions the connected piston can remain stuck so that the suction
stroke is not performed or is not completely performed.
The return brace which is alternatively used and which embraces all
piston rods is an expensive component, in particular in large machines, and
also requires a large structural volume for the entire eccentric drive
mechanism.
DE 85 21 520 describes a multi-cylinder diaphragm pump having a
plurality of diaphragm pump heads which each have a diaphragm actuable
by a hydraulic piston. Here the pump drive is effected by way of a
connecting rod-eccentric arrangement. The connecting rod is rotatably
coupled both to the piston or the piston rod and also to the eccentric shaft
whereby the drive mechanism is expensive to manufacture.
US No 5 368 451 describes a corresponding arrangement with three
hydraulic cylinders, in which the piston rod is urged against the eccentric
surface by means of a return spring.
DE 196 26 938 Al also describes a star-shaped piston-cylinder
arrangement in which the shaft is surrounded by radially oriented cylinders
in which are arranged displaceable pistons connected to the shaft by
connecting rods by way of an eccentric.
Taking the described state of the art as the basic starting point the
object of the present invention is to provide a corresponding drive
mechanism which avoids or at least reduces the described disadvantages.
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According to the invention that object is attained in that the eccentric
shaft and the piston rod are connected together by way of a sliding unit
guide. A sliding unit guide comprises a sliding unit having a slot, a land or
a groove, and a sliding block of corresponding configuration which is
positively guided by the sliding unit.
The use of a sliding unit guide makes it possible to dispense with
connecting rods, which reduces the costs of the drive mechanism and also
makes it possible for example for a diaphragm pump equipped with such a
drive mechanism to be made smaller as now the pistons guided in the
metering cylinders can be coupled directly to the eccentric shaft without a
connecting rod being required.
In a preferred embodiment all piston rods lie in one plane, wherein
particularly preferably the piston rods are arranged in a star configuration.
The term star configuration in accordance with the present application is
used to mean that the piston rods are equally spaced from each other in
the peripheral direction of the eccentric shaft. In other words, adjacent
piston rods respectively include the same angle in a projection on a plane
perpendicularly to the eccentric shaft.
In a further preferred embodiment it is provided that the sliding unit
guide is of such a configuration that the eccentric shaft and the piston rods
are connected together in positively locking relationship in a first direction
in space, preferably also in a second direction in space arranged
perpendicularly thereto, while a relative movement in a third direction in
space which is arranged perpendicularly to the first and second directions in
space is possible.
For example the sliding unit can be in the form of a T-groove and the
sliding block can be in the form of a suitably matched sliding block. It has
been found in that respect that the sliding unit is preferably arranged on
the piston rod and the sliding blocks are preferably fixed to the eccentric
shaft.
By way of example the eccentric shaft can be connected to a sliding
element (for example rotatably) which has the sliding units or the sliding
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blocks, wherein the sliding units or the sliding blocks lie on the boundary
surfaces of a regular polygon with n corners.
In that respect preferably n is an integral multiple of m. It is best for
n = m.
It has further been found that the sliding unit is preferably made
from hardened steel. The sliding block is best made from a copper alloy,
preferably bronze to permit movement of the sliding block in the sliding
unit, with as low friction as possible.
The multi-piston drive mechanism according to the invention
eliminates the disadvantages set forth in the opening part of this
specification in that the piston forces both for the pressure stroke and also
for the suction stroke are transmitted to the individual piston rods directly
by the eccentric sliding unit which is rotatably connected to the eccentric
shaft, wherein additional components such as for example an expensive
return rod or connecting rods are eliminated and thus the structural size of
the overall drive mechanism can be markedly reduced.
Further advantages, features and possible uses will be clearly
apparent from the description hereinafter of preferred embodiments and
the associated Figures in which:
Figure 1 shows a sectional view of a first embodiment of an eccentric
sliding unit drive mechanism according to the invention,
Figure 2 shows a further sectional view perpendicularly to the view in
Figure 1,
Figures 3a - c show three variants of the drive mechanism according
to the invention, and
Figures 4a+b and 5a+b show various embodiments of the connection
between the piston rod and the sliding element.
In the embodiment shown in Figures 1 and 2 the drive mechanism
serves to drive a three-cylinder machine. The drive mechanism thus has
three piston rods 1 which lie in one plane and which are arranged displaced
relative to each other through 1200. The eccentric shaft 2 is rotatably
movably connected to an eccentric sliding unit. When the eccentric shaft is
rotated about the axis 12 the center point 11 of the eccentric sliding unit
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will move on the circle denoted by reference 13. In other words the
eccentric sliding unit performs a translatory circular movement. The sliding
element 6 is preferably triangular, wherein the sliding or groove blocks are
arranged on the three sides of the triangle, which have slide surfaces 8.
The piston rods 1 have corresponding slide shoes 5 which serve as a sliding
unit. As can be seen in particular from Figure 1 the slide shoe 5 embraces
the sliding blocks of the sliding element 6 so that the slide surfaces 8 of
the
sliding blocks bear against the slide surfaces 7 of the sliding unit. The
sliding blocks of the sliding element 6 are thus embraced by the slide shoe
5 in positively locking relationship. Upon rotation of the shaft 2 the slide
shoes 5 will slide along the slide surfaces 8 of the sliding blocks. That
structure provides that almost no transverse forces are applied to the
piston rods 1 by the eccentric shaft.
The extremely compact structure of the drive mechanism can be
clearly seen.
Figures 3a through 3c show three different embodiments of the
invention. Figure 3a shows a two-cylinder drive. The drive mechanism
therefore has only two piston rods 1. The sliding element 6' is here of a
rectangular shape, wherein it is only at two opposite sides of the rectangle
that there are arranged corresponding sliding blocks which are provided
with slide surfaces and which are embraced by the slide shoes 5 of the
piston rods 1. Upon rotation of the shaft the center point 11 of the sliding
element 6' will move along the circle 13.
Figure 3b shows the embodiment already known from Figures 1 and
2, with three cylinders.
Figure 3c shows a four-cylinder drive. The sliding element 6" is
similar to the sliding element 6' of the embodiment of Figure 3a, but in this
case arranged at all four sides of the square sliding element 6" are
corresponding sliding blocks carrying slide surfaces 11, which are
respectively embraced by a slide shoe 5 of one of the four piston rods 1.
Figures 4 and 5 show special embodiments of the slide shoes 5.
Figures 4a and 4b show a view on an enlarged scale of the sliding
unit guide. The piston rods 1 at their end have a pressure plate 5' which
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together with the restraint claws 14 form the slide shoe. The restraint
claws 14 are fixed to the pressure plate 5' by means of a screw. In the
embodiment shown in Figure 4a the restraint claw 14 is screwed at the end
face onto the pressure plate 5'.
In the embodiment shown in Figure 4b the restraint claw 14 is of a
U-shaped configuration so that it embraces both the sliding block and also
the pressure plate 5'. For fixing purposes the claw 14 is then screwed to
the pressure plate 5' from behind, that is to say from the side thereof, that
is remote from the sliding block.
Figures 5a and 5b show embodiments in which the restraint claws 14
are screwed to the peripherally extending edge of the pressure plate 5'. In
the embodiment in Figure 5b both restraint claws 5' are connected together
by means of a bolt and suitable fitting screws 15.
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List of references
1 piston rods
2 eccentric shaft
slide shoe
5 5' slide shoe pressure plate
6, 6', 6" sliding element
7 slide surfaces of the sliding unit
8 slide surfaces of the sliding blocks
circle
10 11 center point of the sliding element
12 axis of the eccentric shaft
13 circle
14 restraint claw
bolt/fitting screw
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