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.

Proceedings of the 2004 , 5:4710-4715, June 30

2004-July 2 2004.