Valve Timing and Area Profile Selection for Hydraulic Pumps and Motors

A significant amount of research has been conducted to select valve timing and area profiles that create efficient and quiet hydraulic pumps and motors. Numerous active valve architectures have been modeled and optimized, but the rationale for the final solution is often unclear. The solution is usually highly dependent on the modeled valve geometry constraints and the duty cycle of the pump or motor for which the valve was optimized. In contrast, this paper proposes a methodology for designing efficient valving that is not constrained to any specific valve geometry, operating point, parameterization, or physical system limitation. An idealized valve area profile is formulated using a piston-cylinder model with variable valve openings. A working fluid that has a pressure dependent bulk modulus is utilized in the model. The valve timing is idealized by constraining it to produce a specified constant pressure drop across the valve. The idealized area profile is synthesized by modeling the piston-cylinder as a pump with passive (check) valves. A representation of the idealized timing is demonstrated for positive pressure differential and positive rotation direction, also known as the first quadrant. The effect of varying pressure on valve timing is shown for the first quadrant, but the trend can be extrapolated for all quadrants of operation. The idealized valve area profile is implemented as fixed valve timing in a pump-motor, meaning the valve area is only a function of the timing angle of the rotating group. Fixed valve timing is preferred to variable valve timing as it can often be implemented mechanically, increasing reliability. The pump-motor is simulated in one rotation direction through a pressure range. Performance is high in pumping operation, but when the pressure differential is reversed, cylinder pressure spikes ensue. Two strategies to modify an idealized valve area profile are presented: timing grooves and a pressure shifted valve timing. Timing grooves reduce pressure spikes and cavitation in the cylinder but generally increase throttling losses. A pressure shifted valve timing has lower throttling energy losses, making it the favored solution.

Control design, implementation, and evaluation for an in-field 500 kW wind turbine with a fixed-displacement hydraulic drivetrain

The business case for compact hydraulic wind turbine drivetrains is becoming ever stronger, as offshore wind turbines are getting larger in terms of size and power output. Hydraulic transmissions are generally employed in high-load systems and form an opportunity for application in multi-megawatt turbines. The Delft Offshore Turbine (DOT) is a hydraulic wind turbine concept replacing conventional drivetrain components with a single seawater pump. Pressurized seawater is directed to a combined Pelton turbine connected to an electrical generator on a central multi-megawatt electricity generation platform. This paper presents the control design, implementation, and evaluation for an intermediate version of the ideal DOT concept: an in-field 500 kW hydraulic wind turbine. It is shown that the overall drivetrain efficiency and controllability are increased by operating the rotor at maximum rotor torque in the below-rated region using a passive torque control strategy. An active valve control scheme is employed and evaluated in near-rated conditions.

Control design, implementation and evaluation for an in-field 500 kW wind turbine with a fixed-displacement hydraulic drivetrain

The business case for compact hydraulic wind turbine drivetrains is becoming ever stronger, as offshore wind turbines are getting larger in terms of size and power output. Hydraulic transmissions are generally employed in high load systems, and form an opportunity for application in multi-megawatt turbines. The Delft Offshore Turbine (DOT) is a hydraulic wind turbine concept replacing conventional drivetrain components with a single seawater pump. Pressurized seawater is directed to a combined Pelton-generator combination on a central multi-megawatt electricity generation platform. This paper presents the control design, implementation and evaluation for an intermediate version of the ideal DOT concept: an in-field 500 kW hydraulic wind turbine. It is shown that the overall drivetrain efficiency and controllability is increased by operating the rotor at maximum rotor torque in the below-rated region using a passive torque control strategy. An active valve control scheme is employed and evaluated in near-rated conditions.

Experimental Study of the Influence of Valve Timing on Hydraulic Motor Efficiency

The timing of the valves of a hydraulic motor plays an important role in determining the throttling energy. To reduce this dominating energy loss, the timing of the valves must allow the fluid in the chamber to be precompressed and decompressed such that there is minimal pressure differential across the transitioning valve. The optimal valve timing to achieve precompression and decompression is a function of the motor displacement, angular velocity, pressure, and air content of the fluid, thus to achieve high efficiency at all conditions, active valve timing is required. The valves in most hydraulic motor architectures are mechanically timed to the piston displacement, rendering it impossible to change the valve timing as a function of operating conditions. This paper presents one novel valve architecture that allows for such processes: a rotary valve that is controlled independently of the piston displacement, enabling active timing control. To validate the concept and test the motor valve at fixed timing and fixed displacement conditions, a prototype valve was installed on a single cylinder 3.5 cc/rev slider-crank piston motor. The nominal timing of the valve was optimized for operation for a pressure of 7 MPa, 2% entrained air by volume, and an angular velocity between 10 and 30 Hz. A model, including the pressure dynamics, leakage, compressibility, check valve dynamics, and geometry dependent parameters is developed, simulated, and compared to the experiment. The experimental system includes instrumentation for measuring the inlet and outlet flow rates, piston position, and pressure in the inlet, outlet, and cylinder. A comparison between the model and experimental data shows good agreement and demonstrate the large impact of valve timing on efficiency.

Research on Piezoelectric Micropump of Combination of Active and Passive Valves

In order to improve the output characteristics of active piezoelectric pump valve, Research on dual-chamber tandem piezoelectric pump of combination of active and passive valves is proposed, And dual-chamber tandem piezoelectric pump of combination of active and passive valves is designed and study. The results show that maximum output flow of dual-chamber tandem piezoelectric pump of combination of active and passive valves is 540ml/min, the most output pressure is 27kPa,the maximum output flow of single-cavity active valve piezoelectric pump is 160ml/min;the most output pressure is 9.8kPa, obtained the conclusion that output flow and output pressure of the dual-chamber tandem of combination of active and passive valve is superior to single chamber active valve piezoelectric pump.