Animal Science

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 brakebased 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.

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 nonmetering 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.

This paper focuses on modeling of torque-biasing devices of a four-wheel-drive system used for improving vehicle stability and handling performance. The proposed driveline system is based on nominal frontwheel-drive operation 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. Kinematic modeling of the torque biasing devices is introduced including stage transitions during the locking stage and the unlocking/slipping stage. Analytical proofs of how torque biasing could be used to influence vehicle yaw dynamics are also included in the paper. A yaw control methodology utilizing the biasing devices is proposed. Finally, co-simulation results with Matlab /Simulink and CarSim show the effectiveness of the torque biasing system in achieving yaw stability control.

Single stage valves have their main spools stroked directly by solenoid actuators. They are cheaper and more reliable. Their use, however, is restricted to low bandwidth and low flow rate applications due to the limitation of the solenoid actuators. In a previous paper, a way proposed to alleviate the need for large solenoids in single stage valves by inducing spool instability using the transient flow forces, hence, improve the spool agility. In this paper, we study the underlying premise that the transient flow forces can be controlled by the "damping length". Models for both steady and transient flow forces that include viscous effects are developed. Various models are analyzed, compared using CFD analysis and correlated to experiments. It was found that the model for the spool dynamics using the various flow force models are consistent with experimental results as long as viscous effects are taken into account. Both magnitude studies and experiments show that "damping lengths" and transient flow forces significantly affect spool agility. CFD studies also indicate that viscosity is an important factor to consider while modeling fluid flow forces.

System parameters for solenoid actuators are important for high performance control and for self-sensing. Due to the nonlinearities in the solenoid actuators, parameter identification procedures that aim to obtain the electro-mechanical property can be complex and time consuming. In this paper, a self-calibration procedure for solenoid actuators in push-pull configurations is proposed. Utilizing the fact that the inductances of the solenoids share the same parameters as those for the electromagnetic force, the parameters for the electromagnetic force can be obtained from the easily obtainable electrical signals such as the voltage and current signals, and two inexpensive on-off sensors. The calibration procedure involves only actuating the solenoid actuator back and forth. Simulation study is presented to verify the method.

An articulated aerial work platform is a type of off highway vehicle with a long/flexible beam to provide temporary access to inaccessable areas. The motivation of the research is to improve productivity and safety of the work platform via advanced control schemes. In this paper, a motion control architecture is presented for trajectory tracking and vibration suppression. By using the sensors integrated in hydraulic power elements, a closed loop coordinated control is presented to allow the end effector of the work platform to track a desired trajectory, thus alleviating the demand on operators' proficiency and improving productivity. In order to reduce the tracking error caused by the beam deflection, a Static Deflection Compensation Controller has been developed. In terms of vehicle safety, it has been observed that vibration associated with the long beam is significant, and the vibration characteristics change according to vehicle geometry. A unique input shaper is presented with the two impulses and the time varying parameters. The benefits are gaining robustness with respect to geometric variation, as well as reducing time delay for better responsiveness. The experimental study validates the controller.

Single stage electrohydraulic flow control valves are currently not suitable in high flow rate and high frequency applications. 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.

Self-sensing refers to extracting the position information from the electromagnetic signals instead of from a physical position sensor. Self-sensing actuator has the benefit of significantly reducing hardware effort. In this paper, we investigate selfsensing actuators applied in direct acing proportional valves. The study is based on the configuration of a dual-solenoid actuator where each solenoid provides the independent single direction force. By considering the electrical dynamics of the solenoids and the nonlinear constraint between the two solenoids , an observer for the flux linkages is obtained. The position estimate is then calculated based on the flux linkage estimates. Both simulation and experiments verify the validity of the proposed algorithm.

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.

The cellulosome of Clostridium thermocellum is a multiprotein complex with endo-and exocellulase, xylanase, ␤-glucanase, and acetyl xylan esterase activities. XynY and XynZ, components of the cellulosome, are composed of several domains including xylanase domains and domains of unknown function (UDs). Database searches revealed that the C-and N-terminal UDs of XynY and XynZ, respectively, have sequence homology with the sequence of a feruloyl esterase of strain PC-2 of the anaerobic fungus Orpinomyces. Purified cellulosomes from C.