Control and Simulation of Torque Converter Lock-up Clutch

Considering the requirements of dynamic performance and quality during the torque converter locking process, a two parameters latch-up control strategy was designed, and a simulation method to study the control performance by use of processor in loop (PIL) simulation technology was proposed. Through the study of the practically applied requirements of a loader, a two parameter lock-up control strategy with turbine speed signal and gear signal as main control parameters was developed. According to the control strategy, the logic diagram of real-time locking and unlocking control of the latch-up clutch was established by using Matlab/Simulink. Then, PIL technology was used to realize the co-simulation of CCS and Simulink. Simulation results show that the latch-up control model is correct and the lock-up clutch can effectively lock and unlock in accordance with the lock-uprule.


1Introduction
The application of torque converter in vehicles greatly simplifies the vehicle handling, improves ride comfort, safety, crossing country and average vehicle speed, but the biggest defect of hydraulic transmission is inefficiency.In order to reduce the fuel consumption of torque converter, a controllable latch-up clutch is installed between the pump wheel and the turbine of the torque converter.When the driving condition of the car reaches the setting target, the lock-up clutch is controlled to lock, the pump wheel is integral to the turbine, and the torque converter then turns into mechanical transmission.To a certain extent, it relieves the problem of low transmission efficiency.
Under the condition that the converter structure type and parameters have been determined, control of lock-up clutch is mainly focus on the improvement of lock-up control quality and the rationality of lock-up rule.The main purpose of lock-up control is to reduce the lock-up impact and improve vehicle dynamic performance.The quality of lock-up process mainly depends on the control during engagement process.In recent years, many domestic scholars have done a great deal of research work in optimizing the lock-up points, realizing multi parameter lock-up control, and control methods such as buffer control by manipulating oil pressure [1][2][3][4].In this study, the lock-uprule of the lock-up clutch of a loader was studied, and the simulation model of the lock-up control was established, and the co-simulation of CCS and Simulink analysis was realized by using PIL detection technology.work on sites where the environments are severe, so two-parameter control was chosen to reduce the impact of the environment on the equipment.In the two-parameter control system, the turbine speed signal and the gear signal were chosen as the main control parameters and the steering signal, the throttle signal and the braking signal were chosen as the auxiliary control parameters.

MATEC
The clutch control can be divided into dynamic locking, economic locking, steering state locking, braking state locking and integrated locking.And the rule of integrated locking has good power performance and fuel economy as well as the operability of the vehicle, and it also ensures great probability for the integrated locking performance of the vehicle for different applications.Therefore, the integrated locking rule was chosen to research on the control system.The integrated locking rule designed of the loader was as follows: 1)Whether the clutch would lock or not is determined by the turbine speed in the braking state; 2)In the steering condition, the unlocking of the latch-up clutch is determined by throttle angle, and the latch-up clutch is not locked when the throttle angle is less than 20%; 3)Locking would prevent the shift from running smoothly when shifting, so the lock-up clutch needs to be unlocked; 4)Whether the latch-up clutch would lock or not can be judged by the rotation speed of the turbine when not to change gear; 5)According to different gears and using purposes, at the first gear, the clutch must be unlocked in order to obtain greater torque for starting, climbing, and high power; at the second gear, the locking is determined by the throttle angle.And when the throttle angle is less than 20%, the clutch is unlocked in order to obtain greater torque; when the throttle angle is more than 20%, whether the clutch would lock or not is judged by the rotation speed of the turbine and the throttle angle in order to make the vehicle more efficient; At the third gear, the clutch needs to be locked in order to make the vehicle get higher speed and larger utilization of power.

Determination of lock-up point of the lock-up clutch
In order to ensure the dynamic performance of the vehicle, double parameters (turbine speed-throttle angle) lock-up rule is usually adopted to select the lock-up points.Under a certain throttle angle, the intersection of two turbine shaft output torque curves under hydraulic conditions (unlocked) and mechanical conditions (locked) respectively is selected, the turbine speed of the intersection point is the lock-up point at the throttle angle.
The torque of the torque converter is the output torque of the pump wheel.It can be expressed by equation ( 1) [5][6].
Where D is the effective diameter of the circulating circle of torque converter, D=0.397m; B is the torque factor;  is the working liquid density (kg/m3), nBis the pump wheel speed (r/min).
The relationship between the torques and rotational speeds of turbine and pump wheel are shown as equation ( 2), (3).
Where M T is the turbine torque (N•m); K is the torque coefficient; M B is the pump torque (N•m);n Ti is the turbine output speed (r/min); n Bi is the pump wheel speed (r/min); i is the speed ratio.From the above analysis, it can be seen that the simulation results meet the control requirements of the lockup clutch.

3.1Establishment of latch-up control model
Web of Conferences 160, 05006 (2018) https://doi.org/10.1051/matecconf/201816005006EECR 2018 2 Lock-up control law of the torque converter 2.1The rule of latch-up control The rule of latch-up control is generally divided into single parameter control and two parameters control.And two-parameter control is a control strategy with two signals as the main control signals and the rest for the auxiliary control signals.In this study, loaders generally

Figure 1 . 2 MATECFigure 1 ,
Figure 1.Schematic diagram of double-parameter power lock-up point design At a certain throttle angle, according to the original data of the engine and formula equation (1), (2), (3), the

Figure 2 .
Figure 2. Simulation model of lock-up clutch control The model of the latch-up control system established in Simulink is shown in Figure 2. Signals such as automatic / manual switch signal, turbine speed signal, shift signal, brake signal, speed signal and turn signal were simulated in Simulink and fed into the lock-up control system in Stateflow.In these signals, the shift signal and the turbine speed signal are the main control signals, while the rest are auxiliary signals.These signals can be set were encapsulated into subsystem Subsystem3.The signals were fed into the logical control in

3 MATECFigure 4 .
Figure 4.In the development board, digital tubes were used to display changes in gears, speed, and other signals.The blocking value and gear changes, etc. were set by the matrix keyboard in the development board.The emulator was used to connect the development board and CCS software to realize the co-simulation of hardware and software.First, the environment variables that Simulink and CCS match were set up in the Windows system.Then, the models those consistent with the development board and emulator were selected, and the simulation model was built in Simulink.The interfaces of the chip used in the simulation model were set.Finally, the model in the Simulink was compiled into the development board by emulator, and the co-simulation of the lock-up control system with Simulink and CCS was realized.

Figure 6 . 4 Conclusions
Figure 6.The simulation output PWM wave in second gear