enhancing the efficiency of a torque converter clutch (tcc)
TRANSCRIPT
Sharon Lin
Stuyvesant High School
Enhancing the Efficiency of a Torque
Converter Clutch Lock-up System
Using a Computational Simulation
AbstractThe torque converter is a fluid coupling that typically replaces the rotating clutch system in automatic transmission, allowing for the engagement and disengagement of power transmission. In order to increase the efficiency of this mechanism, the torque converter may include a clutch lock-up system, directly connecting the engine to the transmission under low-speed conditions. The goal of the study was to develop a mathematical and computational model that would accurate reflect the system dynamics of a typical torque converter clutch lock-up system in order to compare the efficiency of the fuel consumption to power and control with those of electric motors used in hybrid and electric cars. Using MATLAB and component libraries, the study will be able to reflect the physics behind the power-on and power-off modes of the torque converter, as well as accurately measure the engine, vehicle, and shaft speed. This will subsequently result in the development of a physical model in order to test out the mechanical viability of using a transmission as opposed to an electric motor in both commercial and high-end electric and hybrid vehicles.
What is a torque converter? Torque converters are an essential component to
many automobiles in the current industry.
Clutch controls used for manual transmission
Vehicles that employ automatic transmission require the torque converter, a fluid coupling, to engage and disengage the power transmission.
Located between the engine’s flexplate and the transmission, where the torque from the engine is delivered to the transmission through the fluid exchange between the impeller and the turbine.
Allows the engine and the transmission to rotate at different speeds, so that they do not have to have disconnected during gearshift.
Allows the engine to run while the vehicle is not moving, as opposed to manual transmissions, where the two components are separate
http://transmissionrepairguy.com
A Typical Torque Converter
What is the TCC?One addition that automobile manufacturers have
recently added to commercial vehicles is the torque
converter clutch (TCC), which minimizes the energy
loss from the torque converter’s fluid flow in a greater
range of vehicular speeds, simultaneously optimizing
the torque multiplication from engine to transmission in
both low-speed and high-speed conditions. The TCC
locks the transmisson (turbine) and the impeller, which
is connected to the engine (torque converter case).
When closed, the engine, transmission, and vehicle
wheel rotate at the same speed, achieving no difference
in speed between the three components and
subsequently, maximal energy retention. Figure 1
shows the various componetns of the TCC. [1]
(Fig. 1) Diagram of the components within a torque converter clutch(TCC) system
Industry Problems
Torque converters help increase the efficiency of
gasoline-powered vehicles, but they are still not
the most efficient engines
Likewise, electric vehicles – heralded for their
efficiency in energy usage, are still criticized for
their inefficiency in the frame of the overall vehicle
industry.
Hybrid cars, however, seem to solve the issue of
creating a fuel-efficient vehicle that is still practical
to use for the average consumer.
Research Question
Is it possible to create a computational simulation
of different vehicles where their resulting
efficiency can be computed simply by inputting
variables that determine the vehicle’s model? If
so, is it possible to accurately draw conclusions
for which types of vehicles remain the most
efficient in the automobile industry, and for which
reasons?
Hypothesis
After designing the computational model, an
analysis will reveal that the reason behind the
hybrid automobile’s success in its fuel efficiency
is due to its dual-engine capabilities, as well as its
ability to maximize the efficiency of both the
electric and the gasoline-powered engines.
Designing the Torque Converter
The two modes of control for the TCC
power-on lock-up and the power-off lock-up, also
known as the coasting lock-up due to the coasting
of the vehicle that may occur depending on the
driver’s controls
Allows for fuel efficiency through coasting at
moderate and high speeds
Inertial force of the vehicle will be able to drive it forward
Fuel into the engine may be reduced or stopped
so long as the vehicular speed is greater than the
idle speed
ProcessThe study conducted implemented a mathematical and graphical model of a standard torque converter clutch lockup system, created in MATLAB, which allows the graphical model to be converted into C code and subsequently into machine code in order to further experiment with more physical components to account for additional factors not accounted for in the physics implementation of the model. Many standard hybrid vehicles do not implement a torque converter because of their necessity to optimize energy use, due to their smaller electric motors, compared to standard gasoline-powered motors. In high-end vehicles, however, the low-speed control and high-speed power that is required for maximal performance presents an issue, especially in the decision to maximize efficiency in power consumption. The computed model thus demonstrates the optimization of the transmission through the use of a torque converter as opposed to electric motors or other similarly functioning components implemented in commercial electric and hybrid vehicles. A system used in electric motors is shown in Figure 2. [3]
(Fig. 2) Diagram of the components of an electric motor systemwithin a commercial hybrid vehicle
Developing the ModelDeveloping the Simulink model would require advanced
physics calculations before setting up the subsystems
that would compute the effect of the torque converter on
the vehicle. As a result, it was necessary to define all of
the separate components that would go into create the
model. As the torque converter utilizes various aspects
of static and dynamic systems, it was most efficient to
split the model into two separate designs - one for the
slipping, in which the two plates would rotate at different
angular velocities, and one for the lockup, in which the
two plates would rotate at the same angular velocity.
The equations necessary to compute the model were
thus determined, and the variables set to generic values
in order to use as a control for the experiment.
Developing the Model (cont.)
After deriving the necessary relationships, modeling
the dual systems was necessary. This was
illustrated through equating the slipping and lock-up
modes, as well as the frictional transitions between
the two as the vehicle went from the two plates
separately spinning to spinning as a single
component when locked. In Simulink, two
subsystems were created within the larger
subsystem of the torque converter. A logic map was
created, connecting the normal force from the
clutch pedal to the friction model (which calculated
the resulting friction on the system), which was then
drawn to the locked and unlocked modes of the
torque converter.
Developing the Model (cont.)The engine torque was also connected to these two models, along with the friction logic, with breaks and indicators set to determine the point at which the model would transition from one mode to the other. Within the larger model, the unlocked subsystem modeled both sides of the clutch, along with the friction torque. Integrator blocks calculate the engine speeds from the equations above, along with resultant vehicular speeds. Multiplication and summation blocks were used to compute the acceleration from the engine torque and clutch capacity.
The locked subsystem was then constructed, with the input variable defined as the engine torque. The speed and input torque were used to compute the acceleration of the system. After the initial model had been created, it was necessary to compare the results to those of other experiments in order to determine the difference in efficiency. For instance, an electric motor from a hybrid vehicle, an electric motor from an electric vehicle, a transmission system from a hybrid vehicle, a transmission system from an electric vehicle, and a standard torque converter with a P-Pi controller added to the design were compared against the results of the standard torque converter.
Comparisons and Results
The following initial values were inputted into our
simulation:
(Fig. 3) The output values from the standard torque converter trial run.
AnalysisFor the electric motor, comparisons were made to a commercially available electric motor. The results concluded that the electric motor’s efficiency decreased with increasing time and torque. This confirmed that the electric motor used in hybrid and electric cars operates best in low-stress conditions. However, the peak efficiency reached by the motor was still greater in lower velocities than that of the torque converter. For the P-Pi controller, the energy consumption at the start of lock-up was more efficient with the controller implemented than without. This was confirmed from comparisons between the P-Pi controller-implemented model outputs and the standard model outputs. In fact, with the enhanced controller, the efficiency of the torque converter even exceeded that of electric motors at higher velocities.
(Fig. 4) Version 1 of a real-time test for a commercially available motor
(Fig. 5) Version 2 of a real-time test for a commercially available motor over a different surface
(Fig. 6) Results from real-time test of hybrid vehicle motor
(Fig. 7) Results from real-time test of Tesla Model 8 motor
ConclusionsThe model of the torque converter clutch lock-up system
successfully calculated the vehicular and engine speeds through
both power-on and power-off modes. It was also able to determine
the points at which the torque would reach its peak, given different
input and output conditions. Compared against graphs of the output
values for electric motors, it was determined that although the
torque converter may be less efficient in its standard model when
compared against the electric motor, in higher velocities it proved to
have a greater efficiency in terms of energy consumption. In
addition, when the P-Pi controller was implemented within the
model, it showed that there was an increase in efficiency prior to
lockup, which compared to the electric motor was also greater.
Acknowledgements
Jason Econome, the Stuyvesant High School
research coordinator for assisting in the physical
presentation of my research for adjudication
Dr. Jeffrey Kivi, Stuyvesant High School
Chemistry Dept., for consultation with the process
of presenting my work in front of a scientific
audience
My parents for their support of my endeavors
Bibliography [1] Lee, D., Ju, H., Lee, H., Rhee, J., Lee, S., and Lee,
Y. Enhanced Coasting Lock-Up of Torque Converter Clutch after Power-Off Up-Shift using Modified P-PI Control, IAENG Proceedings of the World Congress on Engineering and Computer Science (WCECS), San Francisco, USA, October 2007.
[2] Usui, T., Okaji, T., Muramatsu, T., and Yamashita, Y., ”Development of a Compact Ultra-Flat Torque Converter Equipped with a High-Performance Damper,” SAE Int. J. Engines 8(3):1374-1378, 2015, doi:10.4271/2015- 01-1088.
[3] Jang, J. D., Lee, I. T. , Kim, W. J., and Chun, D. M., ”Effect of a Piston Hole Under the Slip Control Condition of the Lock-Up Clutch in a Torque Converter,” International Journal of Automotive Technology 16(1):139- 144, 2015 doi:10.1007/s12239-015-0015-4.
Bibliography (cont.)
[4] Lin, C. C., Peng, H., Grizzle, J.W., Kang, J.
M.,”Power Management Strategy for a Parallel
Hybrid Electric Truck,” Control Systems
Technology, IEEE Transactions 11(6):839-849,
Nov. 2003, doi: 10.1109/TCST.2003.815606.
[5] Lin, C. C., Peng, H., Grizzle, J.W., ”A
Stochastic Control Strategy for Hybrid Electric
Vehicles,” American Control Conference, 2004.
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