Mohammad Pournazeri

An Efficient Lift Control Technique in Electro-hydraulic Camless Valvetrain Using Variable Speed Hydraulic Pump

Significant improvement in fuel consumption, torque delivery and emission could be achieved through flexible control of the valve timings, duration and lift. In most existing electrohydraulic variable valve actuation systems, the desired valve lift within every engine cycle is achieved by accurately controlling of the solenoid-valve opening interval; however, due to slow response time, precision control of these valves is difficult particularly during higher engine speeds. In this paper a new lift control strategy is proposed based on the hydraulic supply pressure and flow control. In this method, in order to control the peak valve lift, the hydraulic pump speed is precisely controlled using a two-input gearbox mechanism. This eliminates the need for precision control of the solenoid valves opening interval within every cycle. To achieve a smooth control signal, it is worthwhile to control the maximum valve lift within few engine cycles rather than every cycle; therefore, instead of using the governing nonlinear differential equations of the mechanism, a novel average model of the system is developed based on energy conservation equations. A non-linear sliding mode controller (SMC) is also designed based on the developed average model and the boundary layer method is used to eliminate the chattering problem. The performance of the proposed controller is then examined through some simulations. Moreover, the new lift control technique is implemented experimentally by reconfiguration of the existing electrohydraulic valve system prototype and empirical results are then compared with those obtained from the simulations.

A Cam-Based Electro-Hydraulic Variable Valve Timing System for Pneumatic Hybrid Engines

In this work, a new type of cam-based variable valve timing system has been proposed based on the “lost motion” principle. Using this mechanism, the problems with the valve transition time and control complexity which are still serious concerns for camless valve train systems are solved. This mechanism not only allows the engine to work at different modes of operation as an air hybrid engine but also enables it for continuous torque management. In this system, the control methodology utilizes a cam position feedback to control the valve opening timing. A combination of hydraulic and mechanical systems was utilized to offer high flexibility and robustness in the engine valve control system. A zero dimensional analysis is also conducted to evaluate the functionality and performance of the proposed system.Copyright

A Robust Lift Control Technique in Electro-Hydraulic Camless Valves Using System Average Model

In electro-hydraulic camless valvetrains, both valve timing and lift are simultaneously controlled through precise control of solenoid actuated servo-valves at each cycle. In fact, the desired maximum lift is obtained by accurate controlling of the servo-valve opening interval. However, at high engine speeds, due to the slow servo-valve response time, concurrent control of both timing and peak lift becomes more difficult and sometimes impossible. In this paper a new valve lift control technique is proposed based on the average model of the mechanism introduced in [1]. Using this method, it is possible to control the valve lift without precise control of the high pressure servo-valve opening interval and the servo-valves are only responsible for controlling the valve timings and duration. This eliminates the need for high precision servo-valves and measuring devices and consequently cut the system cost. In contrast to the existing lift control methods in which the maximum lift should be repeatedly controlled within each cycle, employing this technique, it is possible to adjust the maximum valve lift after few engine cycles. To this end, an average model of the system is developed based on system energy balance and a non-linear sliding mode controller is designed and implemented on the proposed mechanism. To compensate for the model uncertainties, the designed sliding mode controller is equipped with adaptive law. A conventional boundary layer method is used to solve the controller chattering problem. Finally, the performance of the proposed lift control technique is evaluated through simulation.Copyright

A New Valve Lift Control Technique in Electrohydraulic Variable Valve Actuation Systems

Besides valve timings and opening duration control, several benefits could be achieved in engine operation if the valve actuation system could control the maximum valve displacement during a particular engine condition. Typically, in most electro-hydraulic variable valve actuation systems (VVA), the maximum valve lift along with valve opening/closing events are adjusted simultaneously by precise control of the spool travel in servo-valves. However, at high engine speeds, concurrent control of timings and peak valve lift becomes difficult and sometimes even impossible due to servo-valve response time limitations. In this paper, a new lift control technique is proposed using a control-valve located in the hydraulic supply line. Using this technique, it is possible to precisely control the valve lift even at high engine speeds. With this mechanism, the control-valve flow area could be adjusted using a low-speed actuator such as an electric motor. In contrast to conventional approaches, where maximum lift is repeatedly controlled within each cycle, valve lift in this technique can be adjusted after few engine cycles, thereby reducing control signal fluctuations and also eliminating the need for ultra-high-speed actuators. The proposed hydraulic VVA system is mathematically modeled, and a non-linear sliding mode controller is designed based on the derived equations. Finally, the performance of the proposed lift control technique is verified under different operating conditions.Copyright

A new electro-hydraulic valvetrain configuration with improved lift controllability

In this paper, a new technique is proposed to control the engine valve lift in electro-hydraulic valvetrains. To decrease the computational costs and controller complexity, an average model of the system is derived based on the energy conservation principle. A Sliding Mode Controller (SMC) is designed based on system average model and its performance is evaluated at different operating conditions. The results show a steady-state tracking error of less than 0.5 mm for the final valve lift. Finally, the mechanism’s robustness and its power consumption are studied and the results are compared with those obtained from the existing mechanisms.

A Robust Variable Valve Actuation System With Energy Recovery Mechanism

In this paper, a new hydraulic variable valve actuation system is proposed. Using this system, the engine valve opening and closing timings and lift are flexibly controlled with two rotary spool valves actuated by the engine crankshaft. High degree of flexibility with less control complexity and high repeatability are the advantages of this system over other camless valvetrains; however, in this system, there is a trade-off between its robustness and power consumption. A numerical model of the system is developed to study the system functionality at different operating conditions. To validate the developed model, the simulation results for a random operating condition are compared with those from the experiments. A sensitivity analysis is done to study the effects of variations in different design parameters on system robustness and power consumption. The results prove that increasing engine valve return-spring stiffness and actuator piston area will reduce the mechanism sensitivity to engine cycle-to-cycle variations; however, this results in poor energy efficiency. Therefore, a neat energy recovery strategy is developed to recuperate a portion of the energy used to compress the engine valve return-spring during valve opening interval. The results show that more than 90% of the extra energy wasted for the sake of system robustness could be regenerated through the proposed energy recovery system.Copyright

Regenerative braking torque control of air hybrid engines with cam-based valvetrains

In this work, a novel air hybrid engine configuration is introduced in which cam-based valvetrain along with three-way and unidirectional valves make the implementation of different engine operational modes possible. In the proposed configuration, an electronic throttle system is used to manage the engine load in both conventional and braking modes. The necessity of engine torque control during regenerative braking is discussed and a lookup table/PI controller is applied to the engine model in GT-Power to control the engine torque at the regenerative mode. It is shown that utilising the proposed configuration, the regenerative braking mode can be simply implemented and the braking torque can be regulated by controlling the throttle angle.

Air Hybrid Engine Torque Control Using Adaptive Sliding Mode Control

In this work, a new air hybrid engine configuration is introduced in which two throttles are used to manage the engine load in three modes of operation i.e. braking, air motor, and conventional mode. A Mean Value Model (MVM) of the engine is developed at braking mode and a new Adaptive Sliding Mode Controller (ASMC), recently proposed in the literature, is applied to control the engine torque at this mode. The results show that the controller performs remarkably well in terms of the robustness, tracking error convergence and disturbance attenuation. Chattering effect is also removed by utilizing the ASMC scheme.Copyright