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Dynamic Modeling and Control of a Novel
Overrunning Clutch Shift-Assistant Transmission for
Wind Turbines
Zhi Geng
Shanghai Macrockets Technology Co., Ltd
Wenmin Zhu
University of shanghai for Science and Technology
Research Article
Keywords: Wind turbines, Clutch, Shift-assistant, Automatic transmission, Shift characteristics
Posted Date: August 13th, 2024
DOI: https://doi.org/10.21203/rs.3.rs-4896075/v1
License: This work is licensed under a Creative Commons Attribution 4.0 International License.
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Additional Declarations: The authors declare no competing interests.
Dynamic Modeling and Control of a Novel Overrunning
Clutch Shift-Assistant Transmission for Wind Turbines
Geng Zhia,∗, Wenmin Zhub
aShanghai Macrockets Technology Co., Ltd, Minhang, Shanghai, 201101, China
bSchool of Mechanical Engineering, University of Shanghai for Science and Technology,
Shanghai, 200093, China
Abstract
A novel automatic transmission that achieves power-on shifting with only one
friction clutch, i.e., an overrunning clutch shift-assistant transmission (OCT) is
developed for wind turbines. This transmission realizes continuous shifting by
alternating power transfer between a friction clutch and an overrunning clutch. To
study the shift smoothness of this automatic transmission, a six-degree-of-freedom
dynamic model of a two-speed transmission was established. A coordinated
control strategy for the clutch and power source during shifting was proposed,
and simulation and test bench studies were conducted. The results show that
the proposed upshift and downshift control strategies can effectively reduce shift
impact, keeping the jerk during shifting within 10 m/s3.
Keywords: Wind turbines, Clutch, Shift-assistant, Automatic transmission,
Shift characteristics
1. Introduction
Gear transmissions have been a crucial component in the evolution of automotive
and renewable energy technologies, offering drivers increased convenience and
improved power transmission performance [1,2]. These systems have undergone
significant advancements, moving from simple hydraulic-controlled units to sophisticated
electronically-managed systems [3]. Traditional automatic transmissions typically
use a torque converter and a set of planetary gears to provide smooth, seamless
gear changes without driver intervention [4]. However, they have historically been
criticized for reduced fuel efficiency compared to manual transmissions. This led
to the development of more advanced systems such as dual-clutch transmissions
(DCTs) and continuously variable transmissions (CVTs), which aim to combine
the convenience of automatic operation with improved efficiency [5,6]. In recent
years, the focus has shifted towards developing transmissions that can provide
smoother shifts, better fuel economy, and enhanced performance, all while meeting
∗Corresponding author
Preprint submitted to Elsevier August 11, 2024
Symbol Definition
TeEngine torque
Tin Transmission input torque
TORC Overrunning clutch torque
TW F C Wet friction clutch torque
Tout Half-shaft output torque
TwWheel output torque
θeEngine crankshaft angle
θin Input shaft angle
θ1ORC power shaft angle
θ2WFC power shaft angle
θout Output shaft angle
θwWheel angle
JeEngine rotating parts inertia
JwEquivalent inertia of the vehicle at the wheel
Jin Equivalent inertia of input shaft
Jout Equivalent inertia of output shaft and
splitter gear, friction clutch, and
differential at the half-shaft
ORC active part at the input shaft
J1Auxiliary power input shaft inertia
J2Main power input shaft inertia
kin Transmission input stiffness
kout Transmission output stiffness
cin Transmission input damping
cout Transmission output damping
i1,i2,i′
11st, 2nd, and 1’ gear ratios
i0Final drive ratio
2
increasingly stringent emissions regulations [7]. This has resulted in a wide array
of transmission technologies, each with its own set of advantages and challenges,
as automakers strive to balance performance, efficiency, and driver satisfaction in
their vehicle designs [8,9].
The practice has proven that eliminating power interruption during gear shifts
is an important means to improve vehicle power and comfort [10,11]. There
are several ways for stepped automatic transmissions (ATs) to achieve power-
on shifting without interruption: Alternating operation of two friction clutches.
Both AT and DCT adopt this shifting method, with DCT using pre-engaged
gear control during shifting [12,13]. Research shows that this shifting method
places high demands on the coordination of the two clutches and the control of
synchronizes. Improper control may lead to problems such as power circulation or
shift shock [14,15,16]. Alternating operation of two overrunning clutches. The
AMT improvement scheme by Zeroshift [17,18] and the CST scheme proposed
by Huang et al. [3] both adopt this shifting method. Research shows [19] that
although this shifting method is more direct, it requires a significant reduction
in the torque transmitted by the main clutch to effectively avoid shift shock.
Alternating operation of the friction clutch and overrunning clutch. This shifting
method was first applied in AT. Aldo et al. [20] proposed a two-speed transmission
scheme for electric vehicles using this shifting method. This transmission can
achieve rapid gear changes without power interruption, and shift shock can also
be controlled within a reasonable range. However, due to structural reasons, this
scheme does not have the possibility of expanding to multi-speed transmissions.
AMT with power compensation device. Yamasaki et al. [21] added a torque assist
device at the end of the AMT input shaft, but this device increased the complexity
of the transmission structure and control. From an economic point of view, this
scheme is not a suitable technology.
Infinitely Variable Transmission (IVT) [22] represents a significant advancement
in power transmission technology, offering a seamless and continuous range of gear
ratios between its highest and lowest limits, including the ability to achieve a zero
output speed (geared neutral) while the input is rotating. Unlike traditional
stepped transmissions or even CVTs, IVTs can provide an infinite number of gear
ratios within their operating range, allowing for optimal engine or motor efficiency
across various operating conditions [23]. The core principle of IVT often involves
a power-split architecture, where power is transmitted through both mechanical
and hydraulic or electrical paths, and then recombined. This design typically
incorporates planetary gear sets, clutches, and often a variation component, which
could be a toroidal, belt-and-pulley, or hydrostatic system. The key advantage
of IVT lies in its ability to maintain the prime mover (engine or motor) at its
most efficient operating point while delivering the required output speed and
torque, thereby enhancing overall system efficiency and performance [24,25]. This
technology has found applications in various fields, from automotive powertrains
to renewable energy systems, particularly in optimizing the energy capture in
wind turbines and tidal current energy converters.
3
Vibration analysis and structural health monitoring (SHM) of gearboxes are
critical aspects of modern mechanical engineering, particularly in the context of
predictive maintenance and system reliability [26,27]. Gearboxes, being complex
mechanical systems with multiple moving parts, are prone to various failure
modes such as tooth wear, pitting, cracking, and bearing defects [28,29,30,
31,32,33]. These issues can manifest as changes in the vibration signature of
the gearbox. Advanced vibration analysis techniques, including time-domain,
frequency-domain, and time-frequency domain methods, are employed to detect
and diagnose these faults in their early stages [34,35,36]. Techniques such as fast
Fourier transform (FFT), wavelet analysis, and empirical mode decomposition are
commonly used to process vibration signals and extract relevant features [37,38,
39,40]. Structural Health Monitoring takes this a step further by implementing
continuous or periodic assessment of the gearbox’s condition using strategically
placed sensors, often accelerometers or acoustic emission sensors [41,42,35]. The
data collected is processed using sophisticated algorithms, sometimes incorporating
machine learning techniques, to identify deviations from normal operating conditions
[43,44,45]. This approach allows for real-time condition assessment, predictive
maintenance scheduling, and ultimately, prevention of catastrophic failures [46,
47]. In industries where gearbox reliability is crucial, such as wind turbines,
aerospace, and heavy machinery, these techniques have become indispensable tools
for ensuring operational efficiency, reducing downtime, and extending equipment
lifespan [43,35,48].
This study proposes a new type of automatic transmission for wind turbines
that uses alternating operation of friction clutch and overrunning clutch, featuring
multi-speed, stepped, and power-on shifting characteristics. The paper describes
the working principle of this type of transmission, establishes a vehicle dynamics
model, analyzes the shifting mechanism of this type of transmission, and conducts
simulation and test bench research.
2. Working Principle of Overrunning Clutch Shift-Assistant Transmission
Wind turbines rely on sophisticated drivetrain systems to convert wind energy
into electrical power. These mechanisms, consisting of interconnected components,
play a crucial role in the efficient operation of turbines. The drivetrain typically
encompasses the rotor hub, main shaft, gearbox, and generator. As wind forces
act upon the blades, the rotor hub initiates rotation, which is then transferred
through the main shaft. In most configurations, a gearbox amplifies the rotational
speed before it reaches the generator. This intricate assembly of parts works in
concert to optimize energy capture and conversion, forming the core of a wind
turbine’s power generation process. The design and performance of drivetrain
systems significantly influence overall turbine efficiency and reliability, making
them a focal point in ongoing research and development efforts within the wind
energy sector.
The overrunning clutch shift-assistant transmission (OCT) utilizes the automatic
4
disengagement and engagement characteristics of the overrunning clutch to achieve
power-on shifting. The OCT adopts a parallel arrangement of the overrunning
clutch and the friction clutch, dividing the power from the engine into several
paths, and completes shifting by switching between different power paths. The
OCT has multiple topological structures, one simple form of which includes an
overrunning clutch (ORC) and a wet friction clutch (WFC). Power is transmitted
to the output shaft separately or jointly through two paths, as shown in Figure 1.
Figure 1: Structure layout of the drivetrain of a wind turbine with the OCT
In Figure 1, the shaft connected to the driven plate of the wet friction clutch
is called the main power input shaft (WFC shaft), on which the drive gears for
5 forward gears and one reverse gear are arranged. The shaft connected to the
inner ring of the overrunning clutch is called the auxiliary shift input shaft (ORC
shaft), on which the drive gears for 4 forward gears are arranged. In the design,
it is ensured that the gear ratios of the 1’, 2’, 3’, and 4’ drive gears correspond to
those of the 1, 2, 3, and 4 drive gears, i.e., ensuring that the gear ratios of each
gear in the auxiliary shifting path are equal to the corresponding gear ratios in
the main power path.
The working principle of the OCT is illustrated by the working process of R,
1, 2, 3, 2, R:
1. Start-up condition. The OCT start-up is similar to a manual transmission.
During start-up, the 1st gear synchronizer is engaged first, and the vehicle starts
by utilizing the sliding friction during the engagement process of the wet friction
clutch.
2. Upshift condition: stage 1 to 2. The OCT shifting process first
requires shift preparation operations, which include switching from 1st to 1’ gear
and pre-engaging 2nd gear. After engaging the 1’ gear synchronizer, the WFC is
quickly disengaged, thus achieving the power switch from 1st to 1’ gear. Since
the gear ratio of 1’ is equal to that of 1st gear, and the engagement of the 1’ gear
synchronizer can be accompanied by WFC slipping, the power switch from 1st
to 1’ gear is easy to achieve. The pre-engagement of 2nd gear requires engaging
5
the 2nd gear synchronizer. After completing the above shift preparation work,
the WFC is slowly engaged, and the OCT enters the upshift working process, as
shown in Figure 2.
Figure 2: OCT shift process and power flow during shift
During the upshift process, power is transmitted jointly through the 1’ gear and
2nd gear paths. Since the drive gears of both gears mesh with the corresponding
gears on the output shaft in the same direction, the power transmitted through
the 1’ gear and 2nd gear paths provides mutual positive thrust. As the WFC
engagement increases, the power transmitted through the 2nd gear path will
continuously increase. When the WFC is engaged to a certain degree, the positive
force on the 1’ gear causes the inner ring speed of the ORC to exceed the outer
ring speed, and the ORC will enter the overrunning state. The 1’ gear stops
transmitting power, and power is only transmitted through the 2nd gear, completing
the gear shift. After all power is transmitted through the 2nd gear, the 1’ gear
synchronizer is disengaged, and the upshift process ends.
3. Upshift condition: stage 2 to 3. The working principle is the same
as the 1 to 2 upshift, which demonstrates that the OCT has the capability for
continuous upshifting.
4. Downshift condition: stage 3 to 2. The OCT downshift operation is
opposite to the upshift, i.e., first completing the power switch from 3rd to 2’ gear,
and then switching power from 2’ to 2nd gear. The specific operation is: while
working in 3rd gear, engage the 2’ gear synchronizer, then slowly disengage the
WFC, gradually reducing the output shaft speed. When the WFC is disengaged
to a certain degree, the ORC enters the locked state, and the 2’ gear begins to
participate in power transmission. Continue disengaging the WFC until completely
disengaged, switching the gear to 2’. The power switch from 2’ to 2nd gear is easy
to achieve and will not be elaborated here.
6
5. Neutral and parking conditions. The OCT’s neutral and parking
operations are similar to those of MT. For example, if the current gear is 2nd,
quickly disengage the WFC, then disengage the 2nd gear synchronizer to complete
the neutral operation. Based on the above description, the OCT can achieve all
functions of a vehicle transmission and does not produce power interruption during
shifting.
3. Dynamic Model of OCT
Based on the characteristics of the OCT transmission system, ignoring the
influence of internal damping and gear meshing stiffness of the transmission, a
6-degree-of-freedom dynamic model of a two-speed drive system is established, as
shown in Figure 3.
Figure 3: Dynamic model of the drivetrain system with the OCT transmission system
3.1. Dynamic Model for Upshift Stage
3.1.1. Shift Preparation Phase
As described in Section 1, the shift preparation phase requires switching from
1st to 1’ gear and pre-engaging 2nd gear. After the 1st to 1’ gear switch operation
is completed, the WFC will be quickly disengaged. At this time, the system power
is only transmitted through the ORC shaft, i.e., the current gear is 1’, and the
dynamic equations of the transmission system are:
Te−Tin =Je¨
θe(1)
Tin −TORC =Jin ¨
θin (2)
TORC −
Tout
i′
1i0
= (J1+Jout
i′2
1i2
0
)¨
θin (3)
Tout −Tw=Jw¨
θw(4)
Tin =kin(θe−θin ) + cin(˙
θe−˙
θin)(5)
Tout =kout(θout −θw) + cout (˙
θout −˙
θw)(6)
7
3.1.2. Torque Phase
From the start of WFC slipping, both WFC and ORC transmit torque, with
the ORC still in the engaged state. The system enters the torque phase, and its
dynamic equations are:
Te−Tin =Je¨
θe(7)
Tin −TORC −TW F C =Jin ¨
θin (8)
i0
i′
1
TORC +i0
i2
TW F C −Tout = ( i2
0
i′2
1
J1+i2
0
i2
2
J2+Jout)¨
θout (9)
Tout −Tw=Jw¨
θw(10)
Tin =kin(θe−θin ) + cin(˙
θe−˙
θin)(11)
Tout =kout(θout −θw) + cout (˙
θout −˙
θw)(12)
3.1.3. Inertia Phase
When the WFC is engaged to a certain degree, the inner and outer ring speeds
of the ORC reach equality. As the WFC continues to engage, the inner ring speed
of the ORC will exceed the outer ring speed, and the ORC overruns. From the
moment the ORC disengages, the system power will be transmitted solely through
the WFC path. At this time, the system enters the inertia phase, and the dynamic
equations are:
Te−Tin =Je¨
θe(13)
Tin −TW F C =Jin ¨
θin (14)
i0
i2
TW F C −Tout = (i2
0
i2
2
J2+Jout)¨
θout (15)
Tout −Tw=Jw¨
θw(16)
Tin =kin(θe−θin ) + cin(˙
θe−˙
θin)(17)
Tout =kout(θout −θw) + cout (˙
θout −˙
θw)(18)
3.2. Dynamic Model for Downshift Stage
3.2.1. Inertia Phase
In the early stage of downshift operation, as the ORC is in a disengaged state,
the system power is entirely transmitted through the WFC. At this time, the
dynamic model is:
Tin −TW F C =Jin ¨
θin (19)
i0
i2
TW F C −Tout = (i2
0
i2
2
J2+Jout)¨
θout (20)
8
3.2.2. Torque Phase
When the WFC is disengaged to a certain degree, the system power is transmitted
jointly by the ORC and WFC. The dynamic equations of the transmission are:
Tin −TORC −TW F C =Jin ¨
θin (21)
i0
i′
1
TORC +i0
i2
TW F C −Tout = ( i2
0
i′2
1
J1+i2
0
i2
2
J2+Jout)¨
θout (22)
3.2.3. Shift Completion Phase
Continue to disengage the WFC until the power is entirely transmitted through
the ORC path. At this time, the transmission is in a stable working state of 1’
gear, and the dynamic equations are:
Tin −TORC =Jin ¨
θin (23)
TORC −
Tout
i′
1i0
= (J1+Jout
i′2
1i2
0
)¨
θin (24)
4. Simulation and Test of OCT Shifting Process
4.1. Shift Control Strategy
OCT upshifting will go through transmission control stages such as shift
preparation, wet friction clutch oil filling, low gear synchronizer disengagement,
etc., along with engine torque control. OCT downshifting will go through transmission
control stages such as shift preparation, wet friction clutch pressure release, high
gear synchronizer disengagement, etc., along with engine speed control.
Figure 4shows the OCT shift control strategy.
As can be seen from Figure 4, during the shifting process, the focus is on the
coordinated control of the wet friction clutch and the engine near the separation
and engagement points of the overrunning clutch, which needs to form a closed-
loop feedback.
4.2. Wet Friction Clutch Oil Pressure Control Law
During the engagement process of the wet friction clutch, the control oil
pressure increases nonlinearly. The control of oil pressure will be divided into
5 processes: pre-filling, pressure callback, slow pressure increase, rapid pressure
increase, and pressure maintenance, as shown in Figure 5.
In Figure 5,p1is the maximum pressure reached during the pre-filling stage,
which ends at time t2. From t2to t3, the oil pressure is called back from p1to p2.
This is because at the end of this stage (i.e., at time t3), the drive piston of the wet
friction clutch will contact the clutch steel plate. Reducing the engagement speed
helps to reduce the impact when the two elements contact. From the moment the
piston pushes the steel plate, the wet friction clutch will experience a transition
9
(a) Upshift control strategy (b) Downshift control strategy
Figure 4: OCT shift control strategy
from viscous torque to rough torque. During this stage, the slope of the torque
transmitted by the wet friction clutch will change. To avoid impact in the drive
system, the clutch control oil pressure should slowly increase during the time
period t3to t4. After the wet friction clutch enters the rough torque transmission
stage, the slope of oil pressure increases, the clutch quickly engages, and after full
engagement, the clutch oil pressure no longer increases, maintaining at pressure
p4.
During the separation process of the wet friction clutch, the pressure release
is divided into four stages: static friction pressure release, sliding friction pressure
release, oil pressure callback, and rapid pressure release, as shown in Figure 6.
In Figure 6,p4is the pressure maintenance pressure of the wet friction clutch
(same as in the filling process). When the downshift command is issued, the wet
friction clutch starts to release pressure, and the oil pressure begins to decrease
from time t1. During the time period t1to t2, the wet friction clutch is in a
fully engaged state, and the friction between the friction plate and the steel plate
is static friction. Reducing the clutch pressure with a larger slope will quickly
reduce the static friction force, allowing the clutch to quickly enter the slip state.
When the oil pressure drops to p5, the clutch begins to enter the sliding friction
stage. During the static-dynamic friction transition, the transmitted torque will
fluctuate due to the influence of clutch friction. Therefore, during the t2to t3
stage, the slope of oil pressure reduction is changed to reduce the drive system
torque impact at this time.
As the degree of separation of the wet friction clutch increases, its transmitted
torque will further decrease, and the overrunning clutch is about to start engaging.
From the research conclusions in Section 4, it can be seen that if the wet friction
clutch separates too quickly at this time, it will cause the speed difference between
10
t1t2t3t4t5
0
P0
P6
P5
P7
P4
Time
Oil Pressure
Figure 5: Oil pressure control law during wet friction clutch engagement
the inner and outer rings of the overrunning clutch to be too large, leading
to a large slope of torque difference when the overrunning clutch engages, and
consequently causing a large shift impact. Therefore, during the t3to t4period,
the oil pressure needs to be called back to ensure that the speed difference between
the inner and outer rings is small when the overrunning clutch engages. After t4,
rapid pressure release occurs until the wet friction clutch is completely separated.
5. Simulation Research
A simulation study was conducted on the dynamic model shown in Figure 3.
A drive system dynamics simulation model was built, with the main parameters
used as shown in Table 1.
Figure 7shows the simulation results of the 1st to 2nd gear upshift process.
In Figure 7, the OCT shift starts at 3s, at which time the wet friction clutch
disengages and the transmission works in 1’ gear. At 4 s, the wet friction clutch
begins to engage, and at this time, the 2nd gear synchronizer has already engaged,
and the transmission enters the shift torque phase. The OCT shift ends at 5s, at
which time the output shaft torque fluctuation ends and the 1’ gear synchronizer
disengages.
Figure 7includes the engagement process of the wet friction clutch and the
automatic disengagement process of the overrunning clutch. In the simulation, a
constant rate of change control method was adopted for the wet friction clutch oil
pressure. The WFC torque change first increases, reaches a maximum overshoot
value, then decreases, and stabilizes after oscillation. Research has found that the
magnitude of torque overshoot depends on the system’s inherent characteristics
and the limiting value of the WFC transmitted torque. The smaller the limiting
value of the WFC torque, the smaller the torque overshoot. To minimize the
11
t1t2t3t4t5
0
P0
P6
P5
P7
P4
Time
Oil Pressure
Figure 6: Oil pressure control law during wet friction clutch disengagement
drive system torque fluctuation as much as possible, it is necessary to reduce
the maximum torque value of the wet friction clutch. However, from a practical
point of view, the wet friction clutch also needs to have a certain torque reserve
coefficient. Therefore, the analysis of input torque can also serve as a method for
designing the structural parameters of the wet friction clutch. The clutch friction
plate designed in this paper has an inner diameter of 145mm, an outer diameter
of 171mm, and a total of 5 plates.
Figure 7also includes the control of engine torque. To ensure shift quality,
the engine begins to reduce torque at 4.3s (start of inertia phase) to adapt to
the torque changes during the shifting process. In Figure 7, the speed of the
overrunning clutch continues to rise after disengagement (4.3 s) until the 1’ gear
synchronizer disengages (5 s), at which point its speed rapidly decreases. During
the process of ORC shaft speed increase, the speed difference between its inner
and outer rings continuously increases. The figure shows that at 5s, the speed
difference between the inner and outer rings is 2287 r/min. From this, it can be
seen that to reduce the speed difference between the inner and outer rings of the
overrunning clutch, the low gear synchronizer needs to be disengaged quickly after
it automatically overruns.
Figure 7shows that during shifting, the OCT output torque exhibits characteristics
of first decreasing, then overshooting, and finally oscillating to stability. The
torque decrease process is relatively short (0.2 s), and the torque value does not
decrease much (400 N·m). This is determined by the rapid automatic disengagement
of the overrunning clutch. The simulation results of the 2nd to 1st gear downshift
process are shown in Figure 8.
Similar to the upshift process, Figure 8includes the main control signals and
the speed and torque change curves of the input and output. In Figure 8, the OCT
12
Table 1: Simulation parameters
Parameter/Unit Value Parameter/Unit Value
Je/ (kg·m2) 0.152 i′
14.133
Jin / (kg·m2) 3.361e-5 i03.824
J1/ (kg·m2) 3.433e-4 ro/ mm 116.5
J2/ (kg·m2) 3.819e-4 ri/ mm 90.5
Jout / kg·m2 2.422e-4 µstatic 0.15
Jw/ (kg·m2) 0.2e2 µdynamic 0.12
i14.133 nW F Cf aces 10
i22.252 lW F C / mm 0.1
µoil / (Pa·s) 0.0981 TORC / (N·m/rad·s-1) 29971
CD0.25 m/ kg 14000
A/ m2 2.5 f0.02
g/ m·s−20.307
shift starts at 10.3 s, at which time the wet friction clutch oil pressure begins to
decrease, but the transmission is still working in 2nd gear. As the wet friction
clutch oil pressure decreases, the torque it transmits begins to decrease at 10.6 s.
The overrunning clutch begins to engage at 11 s, and the shift ends at 11.4 s, at
which time the output shaft torque fluctuation ends.
Figure 8includes the disengagement process of the wet friction clutch and the
automatic engagement process of the overrunning clutch. In the simulation, the
pressure release process of the wet friction clutch is controlled, which includes
rapid pressure release (10.3 s to 10.6 s), slow pressure release (10.6 s to 11.05 s),
compensatory pressure increase (11.05 s to 11.1 s), and complete pressure release
(11.1 s to 12 s). The compensatory pressure increase method is adopted in the
clutch separation control because the overrunning clutch engages rigidly at this
time. Continuing to release pressure would cause drive system impact. At this
time, a slight engagement of the wet friction clutch to transmit torque would
effectively reduce the torque overshoot of the output shaft. The compensatory
pressure increase control process is shown in Figure 9.
6. Test Bench Results
Based on the above research on the OCT principle model, a two-speed OCT
test bench with upshift and downshift capabilities was set up. The gear ratios for
the two speeds are 1.13 and 0.78, respectively. The working principle of the test
bench is shown in Figure 10.
The test results are shown in Figure 11. The figure includes the input shaft
speed and output shaft torque for both upshift and downshift. As can be seen
from Figure 11, the transmission output torque during shifting shows a trend
of decrease, overshoot, and oscillation to stability. The upshift and downshift
control tests effectively ensured the smoothness of the drive system shifting. This
13
Figure 7: Dynamic simulation results of 1st to 2nd gear upshift process
Figure 8: Dynamic simulation results of 2nd to 1st gear downshift process
is consistent with the trend of the simulation calculation results, indicating that
the simulation calculation and test results are in agreement, and the shift control
strategy is effective.
14
Figure 9: Compensatory torque increase control of the clutch during downshift
Figure 10: Two-speed OCT test bench
7. Conclusion
Through the research on the Overrunning Clutch Shift-assistant Transmission
in this paper, the following conclusions are drawn:
(1) OCT can achieve continuous power-on shifting and has the basis for development
into a multi-speed automatic transmission.
(2) During OCT shifting, due to the influence of the automatic disengagement
and engagement characteristics of the overrunning clutch, a certain impact will
be produced.
(3) The coordinated control strategy of input torque and clutch can effectively
reduce the impact during shifting.
CRediT authorship contribution statement
Geng Zhi: Conceptualization, Methodology, Investigation, Writing – original
draft. Gang Li: Conceptualization, Methodology, Investigation, Software, Writing
– review & editing, Supervision, Project administration, Funding acquisition.
Wenmin Zhu: Conceptualization, Methodology, Investigation.
15
Figure 11: OCT upshift and downshift test results
Declaration of competing interest
The authors declare that they have no known competing financial interests or
personal relationships that could have appeared to influence the work reported in
this paper.
Acknowledgements
The authors are grateful for the financial support from the National Science
Foundation under Grant No. 2329791.
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