The mechanical efficiency of the current continuously variable transmission (CVT) suffers from high pump loss induced by a high-pressure system. A novel wedge mechanism is designed into the CVT clamp actuation system to generate the majority of clamp force mechanically. Therefore, the hydraulic system can operate at a low-pressure level most of the time, and the pump loss is greatly reduced to improve the CVT's mechanical efficiency. Through dynamic analysis and design optimization, 90% of clamp force is contributed by the wedge mechanism and the rest of the 10% is generated by a conventional hydraulic system. The optimal design is validated through dynamic modeling using Siemens Virtual.Lab software by simulating the wedge clamp force generation, ratio change dynamics, and system response under tip-in conditions. After that, we built prototype components that target 70% of the clamp force contributed by the wedge mechanism and tested them on a transmission dynamometer. The testing results validated the design with reduced hydraulic pressure, the continuous variable unit (CVU) has above 96% peak efficiency and good ratio change capability. It maintains a stable ratio under different vehicle dynamics conditions, such as engine fire torque pulse, pothole, and engine braking. Fuel economy (FE) evaluation is performed under two scenarios with the Federal Test Procedure (FTP) driving cycle. Assuming 70% of pump loss reduction, the composite FE can be improved by 3.4%. More aggressively, assuming 90% of pump loss reduction, the FE improvement can be 4.4%. However, the major challenge of this concept for automotive application is the reverse gear function because the wedge mechanism can only work unidirectionally. A further consideration is needed such as moving the planetary gearset downstream of the CVU so that the wedge does not need to work bidirectionally.

Clutch-to-clutch shift technology is a key enabler for fast and smooth gearshift for multi gear transmissions. However, conventional hydraulic actuation systems for clutches have drawbacks of oil leakage and low efficiency. Electromechanical devices including wedge mechanism offer potential alternative actuators. The previous studies on the wedge emphasize on self-reinforcement, but neglect self-weakened phenomenon. In this paper, a novel dual-wedge mechanism is proposed to exert self-reinforcement and avoid self-weakened effect by selecting a correct working slope. The design concept and physical structure are thoroughly described. Dynamic models for the actuation system and vehicle powertrain are built for performance validation. The results show that the normal force generated by the wedge under self-reinforced case is 2.74 times that under self-weakened case. Using the same amount of the driving motor current, the upshift can be successfully completed in 0.78s when the correct slope is used; however, it fails to engage the clutch when the incorrect slope is used due to self-weakened effect. So does the downshift. Moreover, the experimental results of the dual-wedge mechanism using the correct slope are comparable to those from the hydraulic actuator of a conventional automatic transmission.

A toothed chain continuously variable transmission concept is studied. By designing positive engagement at top overdrive ratio, we explored the potential to improve CVT mechanical efficiency. The low cost solution could improve fuel economy by 0.7% in FTP composite cycle. Preliminary multi-body dynamic simulation is also completed using VL-Motion to concept-proof the technical feasibility of disengagement and engagement. To address the noise issue resulted from abandoning the random pitch design in production chain, we proposed an alternate chain pitch sequence but more experimental data is required to validate the design.

Clutch-to-clutch shift technology is a key enabler for fast and smooth gear shift process for multi gear transmissions. However, conventional hydraulic actuation systems for clutches have drawbacks of low efficiency, oil leakage and inadequate robustness. Electromechanical devices offer potential alternative actuators. In this paper, a novel motor driven wedge-based clutch actuator, featuring self-reinforcement, is proposed. The design concept and physical structure are thoroughly described. Dynamic models for the actuation system and vehicle powertrain are validated by experiments. Upshift and downshift processes at different engine throttle openings, clutch clearances and friction coefficients are discussed. The results show that, the self-reinforcement ratio is tested as 9.6; at the same time, the shift quality is comparable to that of the conventional hydraulic actuated clutch in automatic transmissions in terms of the shift duration (about 1 s) and vehicle jerk (<10 m/s3). Taking advantage of fast response of the actuation DC motor, the wedge-based actuator is robust dealing with uncertain clutch clearance and friction coefficient. Therefore, the wedge-based clutch actuator has potential to provide acceptable performance for clutch-to-clutch shift.

This paper focuses on a physics-based model of a chain CVT. The study starts from kinematics of an infinitely small chain segment, and then investigates the fundamental dynamics of the chain segment. A speed-dependent continuous friction model is employed that accounts for both micro-slip and macro-slip conditions. Pulley axial dynamics is studied and is coupled with chain segment radial movement. The classical pulley deformation (Sattler's model) is included in the model. Simulation results show that pulley deformation plays an important role in defining the chain CVT dynamics. Unlike a rigid pulley, sliding angle with a deformable pulley is not a constant. Internal forces like chain tension and normal contact force are not monotonic function of angular position within the wrap. The simulation results compare well, qualitatively and quantitatively, with data published in literature and clamp force ratio (KpKs) values from dynamometer testing.

The wedge clutch utilizes self-reinforcement feature to amplify the driving torque, however, the input variation is also amplified which makes the system more sensitive to variation of the system parameters and working conditions. In this paper, a self-tuning PID gain parameter is proposed to track the clutch speed difference. The Lyapunov theory is applied in the self-tuning adaptive control to ensure the control system stability. Finally, simulation and experiment demonstrate that the proposed controller has good robustness, improving the shift performance of the wedge clutch under different system parameters and operating conditions.

Electrification technology is becoming increasingly popular in the actuation system of modern vehicles. A novel wedge-clutch-based actuation system driven by a motor is developed. The wedge clutch, which features a self-reinforcement function, can apply a large normal force on the clutch plates while requiring a small motor torque. However, the self-reinforcement feature results in a different dynamic behaviour of the vehicle driveline; therefore, careful control is needed during clutch engagement. A detailed analysis is performed to describe the different challenges of a wedge clutch in comparison with those of a conventional clutch. Based on the integrated engine and transmission control method, a new method of combined control of the motor actuation torque and the engine torque is proposed to improve the shift quality. The proposed control method is validated on a specialized transmission dynamometer by emulating the change from first-gear power to second-gear power in upshift vehicle conditions. The experimental results present how the shift quality of the wedge clutch is improved significantly by introducing the control method. Not only is the maximum transmission output torque about 25.5% smaller, but also the slipping energy is reduced by about 35.1%, which contributes to a smaller temperature rise on the clutch plates. Also, the smaller motor actuation torque has the potential to downsize the electric actuator further and to decrease its power consumption.

A wedge clutch with unique features of self-reinforcement and small actuation force was designed. Its self-reinforcement feature, associated with different factors such as the wedge angle and friction coefficient, brings different dynamics and unstable problem with improper parameters. To analyze this system, a complete mathematical model of the actuation system is built, which includes the DC motor, the wedge mechanism, and the actuated clutch pack. By considering several nonlinear factors, such as the slip-stick friction and the contact or not of the clutch plates, the system is piecewise linear. Through the stability analysis of the linearized system in clutch slipping phase, the stable condition of the designed parameters is obtained as α>arctan⁡(μc). The mathematical model of the actuation system is validated by prototype testing. And with the validated model, the system dynamics in both stable and unstable conditions is investigated and discussed in engineering side.

A wedge clutch with a wedge ramp transfers the tangential force into an axial force. It has unique features of self-reinforcement, and can be packaged into tight spaces. This wedge clutch is developed to apply to an automatic transmission as an implementation example.The slipping decay time is found to be critical for the shifting quality. This paper focuses on the experimental study and control of slipping decay time of the wedge clutch through the influencing factors. The mechanical system of the wedge clutch applied in an automatic transmission is described and the sensors for measuring signals are installed. A transmission dynamometer is set up for experiments.The torque magnitude and direction of the motor motion are considered as actuation factors; the driveline input speed, load torque, and oil temperatures are considered as the driveline factors. The results show how influencing factors affect the slipping decay time during gear shifting.

In this paper, a fuzzy adaptive control law for switching traction and braking systems to stop a hybrid electric bus is proposed. Moreover, the fuzzy adaptive controller takes the actuator constraints into account. Also, online estimation of external disturbance has been used in the design of control law for the robustness of the controller. The stability and convergence properties of the longitudinal brake controller are analytically proved by using Lyapunov stability theory and Barbalat?s lemma. The proposed algorithm is examined for platoon performance. The results of numerical simulation and processor-in-loop simulation demonstrate the control stability of trajectory tracking.

Mechanical press is a machine tool suitable for cold stamping processes such as,drawing,forming,bending,punching,etc.First,the current press linkages were categorized.Then,a modular performance analysis method was proposed based on the Assur's groups,based on which a modular program was constructed for the kinematic performance analysis of multi-link mechanical presses.Finally,two examples,i.e.,six-link double-knuckle press and eight-link double-knuckle servo press,were given to illustrate the proposed method and program.The research is helpful to the linkage design of multi-link mechanical presses.