Qinghui Yuan

On the Use of Torque-Biasing Systems for Electronic Stability Control: Limitations and Possibilities

This brief paper focuses on the concept of utilizing torque-biasing systems on a four-wheel drive vehicle for improving vehicle stability and handling performance. In contrast to brake-based yaw stability control systems, torque biasing has the potential to provide yaw stability control without slowing down the longitudinal response of the vehicle. An inexpensive system configuration is considered in which the driveline is based on front-wheel drive with on-demand transfer of torque to the rear. The torque-biasing components of the system are an electronically controlled center coupler and a rear electronically controlled limited slip differential. First, modeling of the torque-biasing devices is briefly introduced. Then, a hierarchical control architecture is presented in which an upper controller determines desired yaw moment for achieving yaw rate and slip angle control. The lower controller attempts to achieve the desired yaw moment using torque biasing. Theoretical analysis shows that transfer of longitudinal tire forces can effectively be used to achieve any desired yaw moment for the vehicle. However, the use of torque biasing cannot always achieve the desired transfer of longitudinal tire forces. Simulations show that the proposed control system can always effectively provide understeering yaw moments but can provide oversteering torque moments only during on-throttle maneuvers. Experimental data show that significant stability improvements are obtained using the proposed system for low-friction slalom maneuvers and a T-junction launch maneuver. The results presented in this brief shed important light on the possibilities and limitations of using torque biasing for vehicle yaw stability control

Using Steady Flow Force for Unstable Valve Design: Modeling and Experiments

In single stage electrohydraulic valves, solenoid actuators are usually used to stroke the main spools directly. They are cheaper and more reliable than multistage valves. Their use, however, is restricted to low bandwidth and low flow rate applications due to the limitation of the solenoid actuators. Our research focuses on alleviating the need for large and expensive solenoids in single stage valves by advantageously using fluid flow forces. For example, in a previous paper, we proposed to improve spool agility by inducing unstable transient flow forces by the use of negative damping lengths. In the present paper, how steady flow forces can be manipulated to improve spool agility is examined through fundamental momentum analysis, CFD analysis, and experimental studies. Particularly, it is found that two often ignored components-viscosity effect and non-metering momentum flux, have strong influence on steady flow forces. For positive damping lengths, viscosity increases the steady flow force, whereas for negative damping lengths, viscosity has the tendency to reduce steady flow forces. Also, by slightly modifying the non-metering port geometry, the non-metering flux can also be manipulated to reduce steady flow force. Therefore, both transient and steady flow forces can be used to improve the agility of single stage electrohydraulic valves. Experimental results confirm the contributions of both transient and steady flow force in improving spool agility.

Modeling and control of two stage twin spool servo-valve for energy-saving

A control strategy of two stage twin spool servovalves in the load-sensing mobile applications is presented. The twin spool valve differs from the conventional valve in that it provides the ability to control flow into and out of valves independently. In this paper, the nonlinear valve model and a control scheme for a two stage twin spool servo-valve are developed featuring energy saving. The multiple sliding surface mode control method is then utilized to accomplish the motion control while regulating back pressure. The simulation verifies that the proposed control scheme for the twin spool valve, can offer the more significant energy-saving even with load-sensing pump application than the traditional proportional valves.

MODELING AND EXPERIMENTAL STUDY OF FLOW FORCES FOR UNSTABLE VALVE DESIGN

Single stage electrohydraulic flow control valves are currently not suitable in high flow rate and high frequency applicaitons. This is due to the very significant flow induced forces and the power/force limitation of electromagnetic actuators that directly stokes the spool. An unstable valve has been proposed that can utilize the flow forces to achieve fast responses at high flow rate. In this paper, we model the flow forces, including both steady and transient, of a directional flow control valve for incompressible and viscous fluid. In particular, the viscosity effect and non-orifice flux are investigated. The new models have been verified by CFD analysis to be more accurate than the old models. The paper also presents a systematic experimental study on the flow forces, in particular on the steady flow forces. The estimates according to our new models, revised slightly due to the limitation of the experiment, are consistent with the experimental results. Both the experimental results and the modeling estimation show that, for an unstable valve with negative damping length, both transient and steady flow forces can help to achieve the higher spool agility. The satisfactory modeling and experimental study on the flow forces give us a grounding for the future research of unstable valve design.Copyright

Multi-level control of hydraulic gerotor motors and pumps

Multi-level control is a novel method introduced for the control of hydraulic motors and pumps. The method is applicable when two-position, electronically controlled valves are connected to each chamber of a gerotor motor or pump. For motors, the multi-level control can directly regulate the torque, similar to torque regulation of a DC electric motor through current control. For pumps, multi-level control can directly regulate the volume flow rate. Multi-level control permits the regulation of hydraulic motors and pumps without the energy loss associated with a flow control valve, or the mechanical complexity associated with a variable displacement device. Regulation is achieved by using computer control to exploit the complete set of valve combinations, creating torque or flow patterns that are not possible with mechanically actuated values

A model free automatic tuning method for a restricted structured controller by using Simultaneous Perturbation Stochastic Approximation (SPSA)

A model free auto tuning algorithm is developed by using simultaneous perturbation stochastic approximation (SPSA). For such a method, plant models are not required. A set of closed loop experiments are conducted to generate data for an online optimization procedure. The optimum of the parameters of the restricted structured controllers will be found via SPSA algorithm. Compared to the conventional gradient approximation methods, SPSA only needs the small number of measurement of the cost function. It will be beneficial to application with high dimensional parameters. In the paper, a cost function is formulated to directly reflect the control performances widely used in industry, like overshoot, settling time and integral of absolute error. Therefore, the proposed auto tuning method will naturally lead to the desired closed loop performance. A case study of auto tuning of spool position control in a twin spool two stage valve is conducted. Both simulation and experimental study in TI C2000 target demonstrate effectiveness of the algorithm.

Dynamic Control of a Distributed Embedded Electro-Hydraulic System

This paper presents the hardware and software architectures, and the control approaches for a distributed embedded electro-hydraulic system, a telescopic handler. The distributed architecture is justified not only by the complexity of the vehicle architecture, consisting of mechanical, electrical and hydraulic components, but also by the existence of multiple types of communication protocols. The distributed architecture enables a hierarchical control strategy with the system-level control algorithms developed in Matlab/Simulink and implemented for the vehicle’s two primary subsystems, work and propel-bywire.

Multi-Level Phase Shift (MLPS) Control Enabled Variable Displacement Gerotor/Geroler

The research focuses on enabling gerotor/geroler, a traditional fixed displacement device, with the variable displacement capability by integrating electronically controlled digital valves and the corresponding control algorithm. Each digital valve controls polarity of each corresponding chamber of the fixed displacement device. A novel Multi-Level Phase Shift (MLPS) control scheme is developed such that the instantaneous displacement of such a system can be controlled. This control law is characteristic of classifying all the possible valve configuration into several displacement families where the peak value within each family would be identical. Given a desired displacement, both displacement family selection and phase shift technology are utilized to achieve better performance. In the experimental study, MLPS control has been verified, and successfully achieves a closed loop velocity tracking control of a hydraulic geroler motor.Copyright

Extension of robust design of unstable valve: diagonally structured uncertainty

A robust design of an unstable valve with diagonally structured uncertainty is addressed in the paper. An approximate solution can be obtained by minimizing the upper bound of the performance criteria via z k iteration. In addition, the quality of this solution can be evaluated by comparing it to a lower bound

Energy-saving control of an unstable valve with a MR brake

In fluid power systems, excessive heat often causes solenoid failure. Heat, as well as useful power of a solenoid, is associated with the current. In this paper, we attempt to alleviate the requirement for the solenoid power, thus reducing the heat generation accordingly. The method we utilize to change the solenoid power requirement is based on unstable valves, which take advantage of fluid induced forces to achieve open loop instability. Previous studies have shown that for unstable valves, the electromagnetic actuator needs to absorb the power generated by the flow forces. Using the dual-solenoid actuator alone as a brake does not imply heat reduction. In this paper, we propose a new type of actuator in which a dual-solenoid actuator is mounted in series with a magneto-rheological (MR) brake. A nonlinear sliding mode optimal controller is then developed to achieve position tracking and energy-saving. Simulation verities that using the proposed actuator and control law, heat generated in the unstable valves can be reduced significantly.