The dissertation focuses on 1) the loss analysis of the high-speed rotary 3-way on/off valve using CFD, 2) sensing, position estimation, and motion control development for the rotary valve spool motions, and 3) the implementation of the virtually variable displacement pump (VVDP) in a direct displacement control hydraulic circuit.
1.3.1 Scope 1
Since the efficiency of the rotary 3-way on/off valve directly affects the efficiency of the VVDP system, an optimal valve should be designed. The design method involves characterizing the operational losses as functions of valve geometries and operating conditions (flow rate, pressure, etc), and framing the valve design problem into an optimization problem to minimize the losses. Four valve losses are considered: fully open throttling loss, transition loss, compressible loss, and leakage loss [71]. Given the complicated flow path inside the valve, existing analytical formulas cannot fully characterize the valve losses. The flow inside the valve will be modeled using CFD. One purpose of the CFD analysis is to develop an analytical modeling of the 3-way valve losses. The other purpose is to design flow paths inside the valve that minimize throttling and compressible losses.
1.3.2 Scope 2
The valve spool can spin and translate axially inside the valve sleeve. The spool an- gular position is sensed using a set of non-contact optical sensors to simplify the valve sealing structure. The sensing range is relatively long (≈ 2.54cm), and the resolution of the sensor is low. The position measurement is detected at irregular time intervals. In this dissertation, we propose an event based Kalman filter, which can provide a continuous time estimate of the spool’s angular position and velocity from event based measurements.
The valve spool’s axial position is also measured using a set of optical sensors. The spool rotary motion corrupts the spool axial position measurement with structure noise. If the spool rotates at a constant speed, the structured noise is a periodic signal. The position feedback control relying on the corrupted spool position measurement degrades the spool position control precision. This dissertation proposes a periodic time varying model to capture the dynamics of the noise, so that the true spool position can be distinguished from the noise, and can be further used in the position feedback control. After estimating the correct spool axial position, a simple linear controller can be derived for spool position stabilization.
To improve the robustness of the spool axial position control performance, a passiv- ity based nonlinear controller is developed that uses a novel pressure dependent fluid compressibility model to define the energy storage function. An energy function that quantifies the “energy” stored in the pressure error is proposed for pressure error regu- lation. The control law is to regulate the storage function to zero, and correspondingly bring the pressure error to zero. The new controller leads to robust control performance for the spool’s axial position.
1.3.3 Scope 3
The last section of this research focuses on the system level control of a single hydraulic actuator. This research utilizes the VVDP described in Fig. 1.1 as a variable displace- ment pump (VDP) in a direct displacement control circuit, which is shown in Fig. 1.9. A passivity based nonlinear controller is developed to accurately control the position and chamber pressures of the actuator. A novel approach to distribute the control effort be- tween the control devices (including the VVDP, a proportional valve, and a directional valve) is proposed. The approach distributes the control effort optimally between the VVDP and the proportional valve according to their control bandwidths. As a result, the valve is operated with a large mean opening area to reduce throttling loss, while the VVDP is operated following a slow varying profile.
1.4
Dissertation Structure
Chapter 2 presents the CFD analysis of the valve flow. Main results include the validation of the orifice equations in predicting the valve pressure drop; a semi-empirical formula developed based on the CFD results to predict the valve center PWM section pressure drop; and the local flow path modification.
Chapter 3 covers the valve spool rotary sensing and estimation. An event based Kalman filter will be presented to estimate the spool angular position and velocity.
Chapter 4 presents the first generation spool axial position sensing, actuation, and control system. The modeling of the structure-based measurement noise is described. The observability of the plant system augmented with the structured noise model is analyzed. In this generation, the valve spool self-spins, and the spool axial position is actuated hydro-statically using a small gerotor pump.
To improve the spool’s axial position performance and to enable the investment of the effect of actuation strategy on valve efficiency, Chapter 5 describes the second generation of the spool driving system, which allows the spool rotary motion to be driven externally. Optimization results show that when the input flow rate through the valve varies, rotating the valve with an external actuator can produce higher efficiency than relying on self-spinning[72]. In the axial direction, the spool is treated as a single chamber actuated cylinder with a pre-loaded return spring. By manipulating the spool axial chamber pressure, we can vary the spool axial position. A passivity based nonlinear controller is developed for this new driving mechanism, which produces a robust and accurate spool position tracking performance.
Chapter 6 describes a direct displacement control, using a VVDP, to manipulate an open circuit double-ended hydraulic cylinder. The control efforts include the VVDP, supply flow to the cylinder supply chamber, a directional valve, and a proportional valve connecting the cylinder return chamber to the tank. A multi-mode controller is designed to enable the piston to track a reference trajectory. The multiple modes are defined based on the cylinder chamber pressures. The controller can guarantee a precise cylinder position tracking performance, and the cylinder pressures can stay bounded.
Finally in Chapter 7, the conclusion and the contributions of this research work are presented. The future research direction is discussed as well.