Fluid-displacement radial piston machine

A fluid-displacement radial piston machine, such as a hydraulic pump or motor, includes an eccentric member which is mounted on a shaft for displacement radially thereof to thereby change the eccentricity of a contact surface of the eccentric member which is engaged by sliding shoes of a plurality of working pistons. An arrangement for displacing the eccentric member includes a piston component which is connected to the eccentric member by two displacing portions and whose piston portion subdivides a compartment of the shaft into two actuating chambers into which pressurized fluid is selectively admitted through respective passages in the shaft and through a rotary transmission interposed between a source of the pressurized fluid and the shaft. One check valve is interposed in each of the passages and interrupts the communication of the respective actuating chamber with the rotary transmission when no pressurized fluid is admitted into any of the passages. A throttling gap may be provided in each of the passages and may be constituted by a control member received in a bore and acting on the respective check valve to open the same when the eccentric member is to be displaced.

BACKGROUND OF THE INVENTION 
The present invention relates to a fluid-displacement machine in general, 
and more particularly to a radial piston machine, such as a hydraulic pump 
or motor. 
There are already known different constructions of fluid-displacement 
radial piston machines, among them such in which the sliding shoes of the 
working pistons slide over the periphery of an eccentric ring which is 
mounted on a shaft and is displaceable radially of the shaft by means of a 
cylinder-and-piston arrangement which is mounted in the shaft. The shaft 
is then supported in a housing of the machine, and a pressurized medium is 
or can be admitted to the cylinder-and-piston arrangement through 
connecting passages in the shaft and through a rotary transmission which 
is interposed between the housing of the machine and the shaft. 
In one conventional fluid-displacement radial piston machine of this type, 
the cylinder-and-piston arrangement includes two mutually independent 
cylinder-and-piston units which are both mounted in the shaft for 
displacement in the radial direction of the shaft and which are oppositely 
displaceable by a hydraulic medium. Each of the cylinder-and-piston units 
includes a displacing piston which is mounted in a separate compartment 
and has an outer end face which abuts the eccentric ring. The inner end 
face of one of the displacing pistons is permanently acted upon by the 
hydraulic medium. The hydraulic medium reaches the actuating chambers of 
the two separate compartments through connecting passages which are 
provided in the shaft, the connecting passages being connected to a 
pressure and to a relief conduit for the hydraulic medium via a rotary 
transmission interposed between the shaft and the machine housing and 
including sealing rings. 
A pronounced disadvantage of this conventional radial piston machine 
resides in the fact that the displacing pistons can only be displaced 
toward and into their respective two end positions. It is impossible to 
obtain a stable intermediate position of the displacing pistons and of the 
eccentric ring of this radial piston machine in view of the permanent 
action of the hydraulic medium on one of the displacing pistons. 
Therefore, the utility of this conventional machine is quite limited and 
this machine can only be used in certain applications and cannot be varied 
at will. It is further disadvantageous that one of the displacing pistons 
is constantly under the full pressure of the hydraulic medium. This has 
the consequence that even the rotary transmission between the machine 
housing and the shaft is always subjected to the full pressure of the 
hydraulic medium during the operation of the machine. As a result of this, 
the leakage loss in the region of the rotary transmission is very high. In 
addition thereto, the sealing rings which are arranged at the region of 
the rotary transmission are permanently loaded by the pressurized 
hydraulic medium, which reflects itself in continuous frictional forces 
which, in turn, results in a considerable wear of the sealing rings, or 
the surfaces with which the sealing rings are in sliding contact, or both. 
Consequently, as a result of the friction on the one hand, and of the 
leakage on the other hand, the mechanical as well as the volumetric 
efficiency of the above-mentioned conventional fluid-displacement radial 
piston machine is substantially reduced. 
SUMMARY OF THE INVENTION 
Accordingly, it is a general object of the present invention to avoid the 
disadvantages of the prior art. 
More particularly, it is an object of the present invention to provide a 
fluid-displacement radial piston machine which is not possessed of the 
disadvantages of the conventional machines of this type. 
A particular object of the present invention is to so design the radial 
piston machine as to keep the leakage losses and the wear in the region of 
the rotary transmission to a minimum. 
A further object of the present invention is to so construct the machine of 
the type here under consideration as to be able to maintain the eccentric 
member thereof in any intermediate position between the terminal positions 
thereof. 
Yet another object of the present invention is to develop a 
fluid-displacement radial piston machine in which it is possible to 
precisely select and maintain the desired position of the eccentric 
member. 
An additional object of the present invention is to devise a radial piston 
machine in which the pressurized fluid which is used for displacing the 
eccentric member need not be permanently supplied to the displacing 
cylinder-and-piston arrangement. 
A concomitant object of the present invention is to provide a radial piston 
machine which is simple in construction, inexpensive to manufacture and to 
operate, and reliable nevertheless. 
In pursuance of these objects and others which will become apparent 
hereafter, one feature of the present invention resides in a 
fluid-displacement radial piston machine which comprises, in combination, 
a support; a shaft mounted on the support for rotation about a rotary 
axis; an eccentric member having a contact surface extending about an 
eccentric axis; means for mounting the eccentric member on the shaft for 
parallel displacement of the eccentric axis radially of the rotary axis, 
including means defining a radially elongated compartment in the shaft and 
a piston component having a piston portion mounted for longitudinal 
displacement in the compartment and sealingly subdividing the same in two 
actuating chambers, and two displacing portions each extending through one 
of the actuating chambers and sealingly radially beyond the shaft and 
connecting the piston portion with the eccentric member; a plurality of 
working pistons each mounted in the support for reciprocation 
substantially radially of the rotary axis and having an engaging surface 
which engages the contact surface of the eccentric member; means for 
displacing the piston component, including means in the shaft for bounding 
two passages each communicating with one of the actuating chambers, a 
pressurized fluid source, and means for communicating the source with a 
selected one of the passages only for a time period required to displace 
the piston component into any selected position thereof relative to the 
shaft, including a rotary transmission interposed between the support and 
the shaft; and two check valves each interposed in one of the passages and 
operative for interrupting the communication of the respective actuating 
chamber with the rotary transmission to maintain the piston component in 
the selected position thereof outside of, and for establishing such 
communication during, the above-mentioned time period. 
When the radial piston machine is constructed in the above-mentioned 
manner, it is now possible, in an advantageous way, not only to accurately 
determine the two terminal positions of the eccentric member but also to 
displace the eccentric member into and maintain the same in any positively 
defined intermediate position between the maximum and minimum eccentricity 
of the eccentric ring, even during the operation of the machine. In this 
connection, it is of a considerable importance that, in the radial piston 
machine of the present invention, the pressurized fluid need be supplied 
to one or the other end face of the piston portion or, in other words, 
into one or the other of the actuating chambers, only during the time 
period when the piston component, together with the eccentric member, is 
being actually displaced in order to change the eccentricity of the 
contact surface of the eccentric member. As a result of this, no leakage 
losses are encountered outside of the time period during which the piston 
components is being actually displaced. The check valves which are so 
arranged as to interrupt the communication of the respective actuating 
chamber with the rotary transmission outside of the above-mentioned time 
period, and to establish such communication during this time period, 
positively prevent the return flow of the fluid so that it is assured that 
the piston component and the eccentric member connected thereto will 
remain in the respectively selected intermediate or terminal position 
thereof for the entire duration of the subsequent operation of the 
machine, that is, until the position of the piston component and, 
consequently, of the eccentric member, is changed again. 
The piston component may include a cylindrical rod, and then the piston 
portion may be an annular collar which is slid onto and rigidly and 
sealingly connected to the cylindrical rod. However, the entire piston 
component may also be made of one piece. The piston portion is sealed with 
respect to the wall bounding the compartment in the shaft, which is 
preferably of a cylindrical configuration, so that it is impossible for 
the fluid to seep from one into the other of the actuating chambers. The 
actuating chambers which adjoin the piston portions are also sealed with 
respect to the outwardly projecting displacing portions of the piston 
component. To achieve this sealing purpose, it is advantageous to utilize 
annular cylinder seals. The piston component is arranged with a small 
axial tolerance play within the eccentric member, but is movable in the 
circumferential as well as in the axial direction of the shaft with a 
relatively free play. The compartment for the piston component can consist 
of a radial bore in the shaft, and an annular insert can be affixed by 
locking rings at the end of the radial bore, being operative for limiting 
the extent of displacement of the piston portion. The annular insert as 
well as the bottom portion of the radial bore are provided with openings 
and annular cylinder seals for the two displacing portions of the piston 
component. 
In order to render possible a slow and exact displacement of the eccentric 
member, a further feature of the present invention provides means for 
defining a throttling gap in each of the above-mentioned passages. These 
throttling gaps avoid a sudden displacement of the eccentric member and 
thus contribute to a protection of the remaining parts of the machine. 
It is further of advantage that the check valves are arranged radially in 
the shaft. This renders it possible, for instance, to achieve a simple and 
easy-to-manufacture configuration of the bores which accommodate the check 
valves. In this connection, it is especially advantageous when the check 
valves are arranged substantially in that portion of the shaft which is 
surrounded by a bearing which mounts the shaft on the support or housing 
of the machine. As a result of this, there is obtained not only an 
advantageous structural configuration of the shaft and of the 
above-mentioned shaft portion, but also a correspondingly advantageous 
configuration of the support or machine housing, and the mutual 
association of the support with the shaft. A particular advantage resides 
in the fact that double fits, which are quite difficult to accurately 
provide, can be avoided in a relatively simple manner. 
According to a further concept of the present invention, the radial piston 
machine further comprises means for opening the check valves for the 
above-mentioned time period, including means defining a control 
compartment in the shaft, a control piston displaceably received in the 
control compartment and subdividing the same in two control chambers, 
means for admitting the pressurized fluid into a selected one of the 
control chambers, and two control members each of which is displaceable by 
the control piston at least toward one of the check valves to displace the 
same toward an open position thereof. The control members can either be 
attached to the control piston, or may only be in an abutting relationship 
therewith. In any event, it is achieved that double fits with the 
drawbacks inherent thereto are avoided. The control piston can be acted by 
the pressurized fluid from each of its sides. The check valves 
advantageously include spherical valve bodies which are pressed by helical 
springs against corresponding seats. A particular advantage of this 
construction of the check valves is that they are simple in construction 
while avoiding leakage of the fluid past the respective check valve. The 
control piston need not have any special seal at its periphery with 
respect to the surface bounding the control compartment. However, the 
configuration and the position of the control piston render it possible to 
provide a leakage-preventing annular cylinder seal at the periphery of the 
control piston. 
The check valves can be incorporated immediately in correspondingly stepped 
radial bores of the shaft. However, an advantageous embodiment of the 
present invention resides in the fact that at least one, but possibly 
both, of the check valves are accommodated in inserts which are sealingly 
affixed in a bore which transversely extends through the shaft. Under the 
latter circumstances, it is possible to provide the bore in a single 
machining operation as a stepless through bore, which is very advantageous 
from the manufacturing viewpoint, and the inserts can be introduced into 
and positionally fixed in this bore by means of locking rings, as 
completely pre-manufactured structural parts incorporating the check 
valves. In addition thereto, the maintenance of the check valve is 
simplified in this construction, inasmuch as these inserts or structural 
units are easily and simply assemblable with and disassemblable from the 
shaft. Furthermore, these units can be made fully symmetrical, which 
simplifies their manufacture and facilitates their mounting. Leakage past 
these inserts is avoided by means of annular cylinder seals which are 
provided at the periphery of the respective inserts. 
Even though the throttling gaps could be arranged anywhere along the course 
of the respective passages, a particularly advantageous facet of the 
present invention resides in the fact that the throttling gaps are defined 
by parts of the check valve. Advantageously, the means which defines the 
control compartment bounds two bores each of which displaceably receives 
one of the control members, these two bores, the two control chambers, and 
the admitting means constituting parts of the passages. Under these 
circumstances, it is especially advantageous when the throttling gap is 
defined by the respective control member in the respective bore receiving 
the same. By properly selecting the dimensions of the control members, on 
the one hand, and their receiving bores, on the other hand, the annular 
throttling gaps defined between the same are insensitive to soiling and 
clogging even at a low flow-through volume and a small play. 
The maximum and minimum terminal position of the eccentric member can be 
determined, in accordance with the present invention, by providing 
abutments in the above-mentioned actuating chambers. It is especially 
advantageous when these abutments are detachable and, in accordance with a 
preferred concept of the present invention, the abutments are discrete 
abutment members insertable into the actuating chambers. 
The present invention further proposes to mount the eccentric member on the 
shaft between a radial flange of the shaft, at least one annular mounting 
element positionally adjustable along the rotary axis, and two parallel 
planar surfaces of the shaft which together confine the eccentric member 
for the radial displacement thereof. In this manner, the planar surfaces 
assure that the eccentric member will not be able to turn about the rotary 
axis relative to the shaft. As a result of this, the eccentric member is 
freely displaceable in the opposite displacement directions, that is, 
radially of the shaft, but is movable in the axial and circumferential 
direction of the shaft only within the framework of the necessary 
tolerance play. Possible wear manifestations can be compensated for by 
readjustment or exchange of the positionally adjustable mounting element. 
One advantageous aspect of the present invention resides in the fact that 
the two end faces of the piston portion of the piston component which 
respectively face the actuating chambers have the same area. However, it 
is also contemplated by the present invention to give the two end faces of 
the piston portion of the piston component different areas. In this event, 
it is advantageous when the end face with the greater area is subjected to 
the influence of the pressurized fluid when the eccentricity of the 
eccentric member is to be reduced. 
The danger of jamming in the region of the rotary transmission and the 
possibility of scoring and seizing are avoided in the framework of the 
present invention in that the shaft portion of the shaft which is received 
in the support is spaced a considerable distance from the support. 
Advantageously, the rotary transmission includes gas-impermeable metallic 
sealing rings which axially define communicating channels in the spacing 
between the shaft and the support, the individual channels separately 
communicating the connecting passages in the shaft with corresponding 
ducts in the support. The relatively huge play is now rendered possible by 
the fact that the rotary transmission is under the influence of the 
pressurized fluid only for the time period during which the eccentric 
member is being actually displaced. Inasmuch as this time period is very 
short under most circumstances, the somewhat higher leakage which occurs 
during the rather limited time period, is quite acceptable. After the 
termination of the displacing operation, the rotary transmission 
immediately becomes depressurized so that, as a result of this, no leakage 
can occur any longer. What is further achieved by this feature is that it 
is no longer necessary to provide oil-guiding grooves in the shaft. On top 
of this, double fits are no longer necessary. 
The pressurized fluid, such as a hydraulic fluid, is admitted to the piston 
component, in accordance with the invention, through admitting conduits 
for the fluid which have interposed therein a closing valve. 
Advantageously, the closing valve is a three-position four-port valve. By 
providing this closing valve, it is assured that the rotary transmission 
is always depressurized after the termination of the displacing operation, 
and thus becomes leak-proof and frictionless. The respective position of 
the piston component is, however, maintained by the check valves for so 
long until the piston component is again displaced into a new position 
following an actuation of the closing valve. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawing.

DETAILED DISCUSSION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawing in detail, and first to FIG. 1 thereof, it may 
be seen that the reference numeral 1 has been used to designate, in toto, 
a housing or support of a fluid-displacement radial piston machine, for 
instance, of a radial piston motor. In the support, there are mounted 
working pistons 2 for reciprocation, in a star-shaped distribution, in 
correspondingly configurated cylinders 3 which extend substantially 
radially. The working pistons 2 have piston shoes 4 which are in sliding 
contact with the outer periphery of an eccentric member 5. The eccentric 
member 5 is mounted on a shaft 7 for radial displacement relative to the 
rotary axis of the shaft. A piston component 6 accomplishes the 
displacement of the eccentric member 5 relative to the shaft 7 and thus 
determines the extent of reciprocation of the working pistons 2. 
The piston component 6 has, in its central longitudinal region, an annular 
collar 8. Two actuating chambers 9 and 10 adjoin the annular collar 8 at 
both sides thereof, the actuating chamber 9 and 10 being respectively 
connected by connecting passages 11 and 12 with the pressure and relief 
ducts 13 and 14 for a fluid, such as a hydraulic fluid, particularly oil. 
The connecting passages 11 and 12 are provided in the shaft 7 and are 
equipped with throttling gaps 15 and 16, as well as with check valves 17 
and 18 which are so arranged and actuated as to open and close in 
dependence on the pressure prevailing in the respective other of the 
connecting passages 11 and 12. The corresponding control conduits are 
indicated with the reference numerals 19 and 20. 
The transmission of the pressurized fluid between the connecting passages 
11 and 12 in the shaft 7 and the ducts 21 and 22 in the support or housing 
1 is achieved by a rotary transmission 23. The commutation of the 
hydraulic working medium is only indicated in a diagrammatic fashion by 
connectors 24 and 25 and by connecting conduits 26 and 27. Thus, ensued 
the admission of the fluid into and expulsion from the working cylinders 
3. A three-position four-port valve 28 is incorporated in the ducts 21 and 
22 between the pressure and relief conduits 13 or 14 and the rotary 
transmission 23, the valve 28 being controllable as to its position either 
manually or by remote control. 
When the three-position four-port valve 28 is moved into its leftward 
terminal position, the pressurized fluid flows through the duct 21, the 
rotary transmission 23, the check valve 17 and the throttling gap 15 into 
the actuating chamber 9 for so long as the three-position four-port valve 
28 remains in its left terminal position. As a result of this, the piston 
component 6 is displaced relative to the shaft 7 and, as a result of the 
contact of two end faces 29 or 30 of the piston component 6 inwardly on 
the eccentric member 5, the latter is correspondingly displaced 
eccentrically with respect to the rotary axis of the shaft 7. 
Simultaneously therewith, the fluid present in the actuating chamber 10 
flows through the connecting passage 12, the check valve 18 which is in 
its open position because of the action of the fluid present in the 
control conduit 20, through the rotary transmission 23, the duct 22 and 
the three-position four-port valve 28 into the relief conduit 14. 
Now, when the three-position four-port valve 28 is moved, after the 
termination of the displacing operation, again into the illustrated 
closing position, the ducts 21 and 22, or the passages 11 and 12 between 
the three-position four-port valve 28 and the actuating chambers 9 or 10, 
become depressurized and, because of the presence of the check valves 17 
and 18, which assume their closed positions, the fluid present in the 
actuating chambers 9 and 10 and in the adjoining sections of the passages 
11 and 12 is prevented from flowing out. Thus, the piston component 6 
remains in its adjusted precisely defined position. 
When the three-position four-port valve 28 is transferred into its right 
hand terminal position, the pressurized fluid flows from the conduit 13 
via the duct 22, the rotary transmission 23, the check valve 18 and the 
throttling gap 16 into the actuating chamber 10 and there displaces the 
piston component 6 for so long in the opposite direction as the 
three-position four-port valve 28 is open. The fluid from the actuating 
chamber 9 flows through the passage 11, the check valve 17 which is held 
open by the action of the fluid present in the control conduit 19, through 
the rotary transmission 23, the duct 21 and the three-position four-port 
valve 28 to the relief conduit 14. 
After the three-position four-port valve 28 is transferred from its right 
terminal position again into the illustrated closing position, the 
passages 11 and 12 and the ducts 21 and 22 between the three-position 
four-port valve 28 and the check valves 17 and 18 again become 
depressurized and the piston component 6 remains in the then assumed 
position thereof, inasmuch as the check valves 17 and 18, which assume 
their closed positions, prevent the flow of the fluid out of the actuating 
chambers 9 and 10 and the sections of the passages 11 and 12 which extend 
between the actuating chambers 9 and 10 and the check valves 17 and 18. 
According to the embodiment of the present invention which is illustrated 
in detail in FIGS. 2 and 3, the shaft 7 is supported in the support or 
housing 1 of the machine by an anti-friction bearing 31, and has a 
cylindrical radial bore 32 of a greater diameter, and a further bore 33 of 
a smaller diameter. These radial bores 32 and 33 receive the cylindrical 
piston component 6 for displacement of the latter in the longitudinal 
direction of the bores 32 and 33. The piston component 6 has end faces 29 
and 30 which abut, with a small play, the inner sides 34 and 35 of the 
eccentric member 5. The diameter of the piston component 6 corresponds to 
that of the radial bore 33 having the smaller diameter. The sealing 
between a displacing portion 36 of the piston component 6 which passes 
through the smaller-diameter bore 33 and the shaft 7 is obtained by means 
of an annular cylinder seal 37 in the shaft 7. 
An annular collar 8 is provided in the central longitudinal region of the 
piston component 6. The annular collar 8 is sealed, at its circumference, 
by means of an annular cylinder seal 38, with respect to the 
larger-diameter radial bore 32. A displacing portion 39 of the piston 
component 6 is sealingly guided in an annular insert 40. This sealing 
action is achieved by means of an annular cylinder seal 41 in the annular 
insert 40. The annular insert 40 is affixed in the bore 32 by locking 
rings 42, and is sealed with respect to the bore 32 by an annular cylinder 
seal 43. 
As indicated in FIG. 3, the terminal positions of the piston component 6 
can be varied by abutment discs 44 and/or 45 which may be exchangeable and 
which may be of different thicknesses. 
The radial guidance of the eccentric member 5 is achieved, on the one hand, 
by a radial flange 46 of the shaft 7, as well as by positionally 
adjustable mounting elements or discs 47 and 48 and, on the other hand, by 
mutually parallel planar surfaces 49 and 50 of the shaft 7 and the 
corresponding planar surfaces 51 and 52 of the eccentric member 5. The 
mounting discs 47 and 48 abut a bearing 53 which surrounds a shaft portion 
54 of the shaft 6 and supports the same in the housing 1. 
The above-mentioned connecting passages 11, 12 communicate with the 
actuating chambers 9 and 10 which are respectively located at the two 
sides of the annular collar 8 of the piston component 6. The check valves 
17 and 18 are incorporated, respectively, in the connecting passages 11 
and 12. The unused end portions of the connecting passages 11 and 12 are 
sealingly closed by plugs 55. The check valves 17 and 18, which consist of 
spherical valve bodies 56 and of helical compression springs 57 which rest 
against respective threaded blocks 58, which are received in stepped 
radial bores of the shaft 7, and of which the check valve 18 is 
incorporated in an insert body 59 while the other check valve 17 is 
immediately received in the stepped bore of the shaft 7, can be opened by 
control members 60 and 61 which are connected with a control piston 62 
that is located centrally in the shaft 7. In the illustrated exemplary 
embodiment of the present invention, the control member 60 is rigidly 
connected to the control piston 62, while the other control member 61 only 
abuts the control piston 62. The control members 60 and 61 are received 
with a substantial play in the respective bores of either the shaft 
portion 54 or the insert body 59, so that the throttling gaps 15 and 16 
are defined between the outer periphery of the respective control member 
60 or 61 and the surface which bounds the bore in which the respective 
control member 60 or 61 is received. 
The control piston 62 separates two control chambers 63 and 64 from one 
another. Connecting passage sections 11' or 12' which are provided in the 
shaft portion 54 of the shaft 7 respectively communicate with the control 
chambers 63 and 64. The connecting passage 11' communicates, in the region 
of the rotary transmission 23, with the duct 21, while the connecting 
passage 12' is similarly in communication with the duct 22. The 
transmission between the passage 11' and the duct 21, on the one hand and 
between the passage 12' and the duct 22, on the other hand, are separated 
from one another and from the environment by hermetically sealing metallic 
sealing rings 65. It can be further ascertained from the drawing that the 
shaft portion 54 is received in the machine housing 1 with a substantial 
play. 
In the modification illustrated in FIG. 4, at an enlarged scale, both of 
the check valves 17 and 18 are incorporated in respective insert bodies 
59, the insert bodies 59 being accommodated in a stepless through 
transverse bore 66 in the shaft portion 54 of the shaft 7. Each of the 
insert bodies 59 is sealed by annular cylinder seals 67 with respect to 
the transverse bore 66. The two insert bodies 59 support each other by 
means of an insert ring 68 which guides the control piston 62 at its 
interior. At their outer peripheries, the insert bodies 59 are affixed in 
the transverse bore 66 by respective locking rings 69. The remainder of 
the configuration of the shaft portion 54 of the shaft 7, as well as the 
configuration and operation of the parts located at the region of the 
eccentric member 5 and of the piston component 6, correspond to those 
illustrated in and discussed in connection with FIGS. 2 and 3. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
constructions differing from the types described above. 
While the invention has been illustrated and described as embodied in a 
fluid-displacement radial piston machine, it is not intended to be limited 
to the details shown, since various modifications and structural changes 
may be made without departing in any way from the spirit of the present 
invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.