Electro-hydraulic Valve System Research Articles

Experimental Study on Hydraulic Pulsation Features of Intelligent Variable Valve System for Auto Energy Saving.

The electrohydraulic valve system can realize continuous variable valve timing and lift using the flexibility of liquid. However, the existing electrohydraulic valve systems usually rely on a high-speed solenoid valve to control the on and off states of the hydraulic circuit, which pushes up the system cost. This paper introduces a continuous hydraulic variable valve timing and lift system with adjustable volume (CVVTL). Unlike the other electrohydraulic valve systems, the CVVTL does not need a high-frequency servo valve to control each valve but adjusts the valve timing and lift by controlling the system volume. However, the maximum operating speed of hydraulic variable valve systems is limited by the inherent pressure fluctuation. To relax the limit, the authors further studied the pressure fluctuation features of the CVVTL system under various conditions and summarized the harms of the fluctuation. After identifying the causes of pressure fluctuation of the CVVTL system, the authors came up with systematic countermeasures to system pressure fluctuation.

Feedforward Plus Feedback Control of an Electro-Hydraulic Valve System Using a Proportional Control Valve

The output feedback signal of the electro-hydraulic valve system (EHVS) affects the activation of its right or left envelope function; thus, even weak measurement noise can cause high-frequency switching between the two envelope functions, leading to chattering in the control input. Consequently, feedforward and feedback controllers in a cascaded configuration generate undesirable chattering in the output signal. We propose a practical and reliable control approach for an EHVS actuated by a proportional control valve. The proposed controller has a parallel structure comprising an inverse generalized Prandtl–Ishlinskii (P–I) model-based feedforward controller, with both hydraulic dead-zone and flow saturation limits, for compensating asymmetric hysteretic behavior. Further, the proposed controller comprises a robust proportional-integral-derivative (PID) feedback controller for achieving robustness against disturbances and noises. The proposed parallel structure is independent of the output feedback of the EHVS. Moreover, the proposed robust PID feedback controller guarantees EHVS stability by precisely selecting the cutoff frequency for the sensitivity and complementary sensitivity functions based on the amplitude spectrum of the inverse-model-based feedforward compensation error. The results verify the high reliability of the proposed EHVS control scheme for the precise control of an EHVS actuated by a proportional control valve in practice.

Parameter Identification for Electrohydraulic Valvetrain Systems

We consider an electrohydraulic valve system (EHVS) model with uncertain parameters that may possibly vary with time. This is a nonlinear third order system consisting of two clearly separated subsystems, one for the piston position and the other for the chamber pressure. The nonlinearities involved are flow-pressure characteristics of the solenoid valves, the pressure dynamics of the chamber due to varying volume, and a variable damping nonlinearity. We develop a parametric model that is linear in the unknown parameters of the system using filtering. We deal with a nonlinear parameterization in the variable damping term using the Taylor approximation. We design a parameter identifier, which employs a continuous-time unnormalized least-squares update law with a forgetting factor. This update law exponentially converges to the true parameters under a persistence of excitation condition, which is satisfied due to the periodic regime of operation of EHVS. We present simulation results that show good following of unknown parameters even with the presence of sensor noise.

Camless hydraulic valve timing system in combustion engines

The paper discusses the control of the operation of combustion engines through a camless electro-hydraulic valve timing system aiming at a lower exhaust emission and increased overall efficiency. The paper presents an electro-hydraulic valve system and a mathematical model of the fluid flow. The model was simulated in Matlab–Simulink for different geometrical parameters of the hydraulic system and electric control parameters in order to obtain a required valve lift and timing in the Toyota Yaris gasoline 1.3 l engine. The paper presents the Simulink model and the results of calculation in Simulink. Additionally, a comparison of engine parameters with a standard cam valve system and those of the camless hydraulic valve timing system have been shown for different engine speeds obtained from the simulation in GT-Power software. The obtained results show a significant increase of the engine torque and efficiency at higher engine speeds for the considered camless system in the Toyota Yaris gasoline engine. The paper showsboth the advantages and disadvantages of the described valve system.

Implementation and Analysis of a Repetitive Controller for an Electro-Hydraulic Engine Valve System

Variable valve actuation plays an important role in modern engine design. Fuel economy, emissions, and power output can be improved through appropriately varying valve lift and timing. One means of independently and continuously adjusting these valve profile parameters is with an electro-hydraulic valve system (EHVS). However, with an EHVS, it is very difficult to achieve the same level of accurate position control that a mechanical cam provides. In particular, the response time delay and the nonlinear dynamics of the hydraulic system can lead to error in valve position control. The paper first describes the identification method used to obtain a mathematical model of the EHVS. Based on the model, two linear feedback controllers are developed and compared. To further improve the tracking performance, a repetitive feed-forward controller is added to augment the feedback controller and the root mean square tracking error is improved to under 40 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu$</tex> </formula> m. Stability and steady-state tracking error variance analyses complete the mathematical framework of this work.

Reduced Order Modeling and Control of an Electrohydraulic Valve System

In novel combustion strategies like HCCI, fully flexible inlet and exhaust valves in terms of lift and timing are required to enable HCCI. In this paper, we explore issues related to control of an electrohydraulic variable valve system. A nonlinear model of an electrohydraulic valve system is linearized and simplified to a reduced order model to overcome numerical stability issues. A model based control algorithm is developed based on the reduced order model. The control algorithm consists of an observer to estimate the unmeasurable states and the disturbance acting on the plant, and permits tracking of any sufficiently smooth bounded trajectory. Numerical simulations and experimental results are presented for a sine wave and for a partial lift profile to indicate the effectiveness of the control algorithm developed.