Article citation information:
Kaššay,
P., Urbanský, M. New designs of variable stiffness couplings. Scientific Journal of Silesian University of
Technology. Series Transport. 2022, 117,
91-101. ISSN: 0209-3324. DOI: https://doi.org/10.20858/sjsutst.2022.117.6.
Peter
KAŠŠAY[1],
Matej URBANSKÝ[2]
NEW
DESIGNS OF VARIABLE STIFFNESS COUPLINGS
Summary. Flexible
couplings are widely used in mechanical drives of transport and other machines.
A fundamental function of flexible shaft couplings regarding torsional
vibration is the optimum tuning of torsional oscillating mechanical systems. At
the authors’ workplace, the focus is on the research and design of
pneumatic couplings, where the torque is transmitted mainly by compressed gas
(air) in their pneumatic flexible elements. The primary advantage of these
couplings is that their mechanical properties can be quickly and effectively
adjusted, especially the dynamic torsional stiffness, by air pressure change
directly while the mechanical system is running. This allows us “to
tune” the properties of the pneumatic coupling according to the current
parameters of the machine drive to avoid resonance and minimize torsional
vibration. Therefore, we tend to refer to them as “pneumatic tuners of
torsional vibration”. This paper aims to present two new types of these
“pneumatic tuners” that were recently granted patent protections,
namely “Pneumatic flexible shaft coupling with hose flexible
element” and “Drum pneumatic flexible shaft coupling”.
Because these pneumatic tuners are not in practical use yet, this paper
describes only their design and supposed benefits.
Keywords: variable
stiffness couplings, pneumatic torsional vibration tuners, design, patents,
properties
1. INTRODUCTION
Nowadays, the vibration and
noise of machines, especially transport machines, are coming to the fore,
especially regarding the health and comfort of humans and also the fatigue and
durability of machines [1, 5, 14, 23]. Therefore,
several novel methods have been developed to improve mechanical drives to solve
these issues. Engines with internal combustion underwent
major modifications for dynamics, efficiency and emissions, for example, [3, 17]. For
torque transmission between rotating shafts, flexible shaft couplings are
commonly used [1, 4, 6, 12, 16, 25, 28]. Each
drive needs a careful selection of flexible coupling based on detailed
torsional analysis, otherwise excessive torsional vibration may appear [1,
5, 7, 16]. The selected coupling should have appropriate mechanical properties.
The primary parameter affecting the size of torsional
vibration is dynamic torsional stiffness.
Various materials (metals, rubber and plastic) are currently used for
manufacturing shaft coupling flexible elements. These
materials of flexible elements are exposed to cyclic loading, which is then
manifested by subsequent fatigue and wear of flexible elements. Consequently, the shaft coupling loses its initial
(nominal) mechanical properties. As such, it cannot fulfil its tasks, the most important being “tuning of the mechanical
system”, which entails minimizing torsional vibration.
The tuning of modern mechanical drives working in a wide range of
working speeds and uneven cylinder operation (uneven fuel supply or deactivated
cylinders) due to efforts to increase efficiency and reduce emissions is even
more problematic. It is hard to select proper flexible shaft coupling (as a
passive vibroisolation element using no additional energy) capable of providing
optimum tuning for such a wide range of operating parameters. To overcome these problems, there are developed passive
tuners with load characteristics or torsional stiffness adapted to the specific
device to which they are applied. Therefore, flexible couplings with
variable stiffness (as a semi-active vibroisolation element capable of changing
its mechanical properties during operation) are currently being developed.
The change of torsional stiffness is currently
possible by some of the existing variable stiffness couplings, for example,
pneumatic flexible shaft couplings [5, 27] and magnetic shaft couplings [15, 24]. Some authors proposed the use of variable
stiffness coupling using magnetorheological elastomers [11, 18] or leaf springs
with variable active length [9]. Elements with variable
torsional stiffness (referred to as “variable stiffness joints” and
“variable stiffness actuators”) are developed in robotics too [26].
They are used mainly for robots working in environments
where the possibility of collision with surrounding objects or humans cannot be
completely avoided; however, it is also possible to use their working
principles for shaft couplings in the field of mechanical drives. These designs use various types of flexible elements, such
as leaf springs with variable active length [2], magnets, cable mechanisms with
preloaded springs [13] and cam mechanisms with preloaded springs [29].
Variable stiffness vibroisolation elements are also used for damping
rectilinear vibration [10, 23].
At our workplace, we research and develop pneumatic flexible shaft
couplings. For this type of shaft coupling, the torque
transmission is provided by compressed air, which is not subject to fatigue and
ageing. A great advantage of these flexible shaft
coupling types, a few of them for which patents were granted can be found in
[19 – 22], is the ability to adjust their torsional stiffness depending
on the air pressure in pneumatic flexible elements. This ensures that the
dynamic torsional stiffness of a pneumatic coupling can be adapted to the
mechanical system’s current operating conditions.
We focused
specifically on tuning mechanical systems (regarding torsional vibration)
during operation, with the application of “pneumatic tuners of torsional
oscillation” as devices for semi-active tuning of torsional vibration. For this purpose,
we have developed our own electronic control systems. This paper presents two
patented types of “pneumatic tuners”:
1.
Pneumatic flexible shaft coupling with hose flexible element
[19],
2.
Drum pneumatic flexible shaft coupling [21].
This
coupling design, as described in the patent [19], uses a novel type of
pneumatic flexible element. It is a hose-shaped
flexible element winding between the supporting surfaces of the
coupling’s hubs (
Fig. 1). Proposed pneumatic shaft coupling with hose flexible
element (
Fig. 1
Fig. 2) consist of two hubs (1, 2) connected flexibly via hose pneumatic flexible element (3).The hose flexible element winds between the support
surfaces of the driving (4) and
driven (5) hub.
Fig. 1. Pneumatic flexible shaft coupling with hose flexible
element [19]
Compressed gaseous medium is filled into the compression volume of the
coupling through a pneumatic plug (6)
which is secured in the opening of the support surface by an adjusting screw (7). The sealing of the pneumatic plug
is solved by sealing rings (8).
Compressed gaseous medium is filled into the coupling’s compression
volume via a filling valve (9). The
pneumatic hose element is fixed to the support surfaces with screws (10) and washers (11).
Due to the relative rotation of the hubs from the neutral position, the
compression volume of the hose flexible element is compressed, thereby ensuring
a flexible torque transmission between the two hubs. The
advantage of this hose flexible element is that the compression volume of the
entire pneumatic coupling has to be sealed only at the location of the
pneumatic plug and the filling valve ensuring the supply of the compressed
gaseous medium. Furthermore, the design of the hose
flexible element allows for quick and easy assembly and dismantling, if
necessary.
Fig. 2. Pneumatic flexible shaft
coupling with hose flexible element
– Detail of the pneumatic plug connection [19]
2.2. Drum pneumatic flexible shaft
coupling
The proposed “Drum pneumatic
flexible shaft coupling” (Fig. 3 Fig. 4) is made up of the driving parts – a driving drum and a driven
part. Between the
driving and driven parts, the coupling's compression volume is situated. The driving drum is made up of a driving flange (1),
segments (2) and a support disc (3). The driven part is made up of a driven
disc body (5), a support disc (4), deformational rollers (6), which are
rotatably mounted on pins (7), rotatably mounted small rollers (8) and
rotatably mounted guiding small rollers (9).
Flexible torque transmission from the driving
drum to the coupling's driven part is ensured by the coupling's compression
volume, which is made up of flexible hollow bodies (10), which are, together
with shaped rigid bodies (11), fastened to the segments (2) of the driving drum. Each shaped rigid body (11) is
undismountably joined with a flexible hollow body (10). Through a
valve (12), which is part of one of the distributing bodies (13), the gaseous
medium can stream in the compression volume of the coupling. By the distributing bodies (13) and connecting hoses (14),
the mutual interconnection of the flexible hollow bodies (10) is ensured. The distributing bodies (13) are fastened to the shaped
rigid bodies (11). Intake ducts (15) are created in
the shaped rigid bodies (11).
|
|
|
|
|
|
Fig. 3. Drum pneumatic
flexible shaft coupling in a partially loaded state
– main view with details
|
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Fig. 4. Drum
pneumatic flexible shaft coupling in a partially loaded state |
If the flexible hollow bodies (10) of the
unloaded shaft coupling are filled through the valve (12), distributing bodies
(13), connecting hoses (14) and intake ducts (15) with gaseous medium (which
suitable overpressure value was set in advance), sprung levers (16), which are
rotatably mounted on pins (7), lean on stoppers (17) and (18). So, the driving drum acquires its basic position towards
the driven part of the coupling. A load torque
causes an angular deflection of the driving drum towards the driven part of the
coupling (Fig. 3) and, consequently, a deformation of the hollow bodies (10) (coupling's
pneumatic flexible elements). The deformation is caused by deformational rollers (6). The deformed
pneumatic flexible elements (10) are wrapped around the driving drum. The gaseous medium compression in the compression volume
is related to the load; therefore, a flexible transmission of a load torque
occurs in the mechanical system.
The
rotatably mounted small rollers (8) ensure that the deformed pneumatic flexible
elements (10) stay in the deformed shape (
Fig. 5) when the coupling is twisted.
Rotatably mounted guiding small rollers (9) guide the pneumatic elements (10)
during rotation of the coupling when a centrifugal force acts on the elements.
The coupling transmits a load torque flexibly
in one direction only. The sprung levers (16) block the twisting of the
coupling in the opposite direction. Because an
over-twisting of the coupling is enabled at an overload, given that the
coupling also acts as a safety coupling in mechanical systems.
We
can see that the coupling is designed so that it is possible to achieve a high
value of the maximum twist angle α (
Fig. 5). This fact
is fundamental to creating a high-flexible coupling.
Fig. 5. The drum pneumatic flexible
shaft coupling at maximum twist angle α
(fully loaded state)
Flexible coupling with very low
relative torsional stiffness k0
can be considered a high-flexible coupling. The k0
can be expressed as follows:
From equation (1), we can see that the k0 is expressed as the ratio
of the kDN (nominal
dynamic torsional stiffness of the coupling) to the MN (nominal torque of the coupling), whereas the kDN value is considered at MN. The
k0 range of commonly used
flexible couplings is 10 ÷ 30 rad-1, whereas
the k0 value of a
high-flexible coupling is lower than 10 rad-1.
If a high-flexible coupling (coupling
2 in
Fig. 6) is applied in a torsional oscillating
mechanical system (TOMS), we can avoid the resonances in the operating speed
range (OSR) of the system and move them to the low speed range far enough below
idle speed nV, for example
[1, 5, 23]. It is possible to get over this low
speed range at the start-up of the TOMS (
Fig. 6). In the
interference diagram of a mechanical system (
Fig.
6), the torsional vibration excitation harmonic component order is marked
as i .
Fig. 6. General interference diagram
If the
drum pneumatic coupling is applied in a mechanical drive system, flexible
torque transmission is possible. Because its torsional stiffness can be
changed, the tuning of TOMS is also possible in diverse operating conditions.
“Pneumatic
flexible shaft coupling with hose flexible element” and “Drum pneumatic flexible
shaft coupling” can be used in mechanical drive systems. Due to their adjustable torsional stiffness, they provide
flexible torque transfer and guarantee system adjustment under various
operating modes.
The
principal benefit of “Pneumatic
flexible shaft coupling with hose flexible element” is that the
compression volume of the entire coupling is sealed only at the location of the
pneumatic plug and the filling valve ensuring the supply of compressed gaseous
medium. Furthermore,
the design of the hose flexible element allows for quick and easy assembly and
dismantling, if necessary.
Considering
the “Drum pneumatic flexible
shaft coupling”, the purpose of the design is to achieve high
flexibility, which corresponds to a very low relative torsional stiffness. A gaseous
media in the compression volume of a pneumatic coupling does not suffer from
ageing; therefore, the initial positive dynamic properties of a pneumatic
coupling are well preserved.
For example, nowadays, in the automotive industry,
high-flexible couplings are commonly used as dual mass flywheels. Therefore, it is possible to assume that the combination
of the benefits of a pneumatic coupling and a high-flexible coupling will
result in the creation of usable machine parts.
We
believe that the two pneumatic couplings described can raise the technological
capability and reliability of the machine where they could be used for the
abovementioned reasons. Therefore, as part of the objectives of our
subsequent grant project, we will build and test the prototypes of the
specified pneumatic couplings.
Accordingly, we plan to focus our
future study on the following issues:
·
Experimentally determining the static and dynamic
operational parameters of the couplings,
·
Formulating the math-physical models of the couplings,
·
Implementing the new couplings into experimental mechanical devices
to test mainly continuous tuning for torsional dynamics. The couplings will be used
for semi-active torsional vibration tuning operated by our advanced electronic
control systems,
·
Developing
and formulating mathematical models of the examined experimental devices,
·
Comparing the measured data with the results of the
mathematical simulation,
·
If necessary, further improve the mentioned
mathematical and physical models.
References
1.
Dmitrieva Valeriya Valer'evna, Pavel
Yevgen'evich Sizin, Aleksey Andreevich Sobyanin. 2021. „Application of
the soft starter for the asynchronous motor of the belt conveyor”. IOP Conference Series: Earth and
Environmental Science 942(1): 012003. DOI: 10.1088/1755-1315/942/1/012003.
Received 10.07.2022; accepted in
revised form 07.10.2022
Scientific Journal of Silesian University of Technology. Series
Transport is licensed under a Creative Commons Attribution 4.0
International License
[1] Faculty of Mechanical Engineering,
Department of Construction and Transport Engineering, Technical University of
Košice, Letná 9 Street, 042 00 Košice, Slovakia. Email:
peter.kassay@tuke.sk. ORCID: https://orcid.org/0000-0003-0405-6266
[2] Faculty of Mechanical Engineering,
Department of Construction and Transport Engineering, Technical University of
Košice, Letná 9 Street, 042 00 Košice, Slovakia. Email:
matej.urbansky@tuke.sk. ORCID: https://orcid.org/0000-0001-7329-6891