Energy Conservation With Variable Displacement Pumps and Motors

In this paper, the load torque on the swashplate of axial piston variable displacement pumps with conical cylinder blocks is studied. At present, general analytical solution for the load torque of axial piston variable displacement pump is not available, which makes the dynamic analysis and controller design an uneasy work. The main contribution of this paper is that the analytical solution of the swashplate torque caused by piston inertia and centrifugal force was derived. First, based on the piston acceleration and centrifugal force, the piston kinematic and dynamic models were developed, the analytical solution of the swashplate torque caused by piston inertia and centrifugal force was derived. In addition, the piston chamber pressure dynamics were established, the pressure distribution in the cylinder bore and the load torque of the swashplate under different working conditions were obtained. Finally, the relationship between the swashplate average load torque and the swashplate angle, swashplate angular velocity, pump load pressure and the pump input shaft velocity was uncovered. It is shown that the swashplate angle has greater influence on the load torque when the pump load pressure is higher, besides, it is interesting to observe that the swashplate angular velocity has a damping influence upon swashplate dynamics which helps to stabilize the swashplate during pump displacement regulation transients.

Download Full-text

Software Enabled Variable Displacement Pumps: Experimental Studies

Fluid Power Systems and Technology ◽

10.1115/imece2006-14973 ◽

2006 ◽

Cited By ~ 10

Author(s):

Michael B. Rannow ◽

Haink C. Tu ◽

Perry Y. Li ◽

Thomas R. Chase

Keyword(s):

Experimental Studies ◽

Check Valve ◽

Design Parameters ◽

Duty Ratio ◽

System Response ◽

Experimental Apparatus ◽

Displacement Pump ◽

Variable Displacement ◽

Valve Control ◽

Variable Displacement Pumps

The majority of hydraulic systems are controlled using a metering valve or the use of variable displacement pumps. Metering valve control is compact and has a high control bandwidth, but it is energy inefficient due to throttling losses. Variable displacement pumps are far more efficient as the pump only produces the required flow, but comes with the cost of additional bulk, sluggish response, and added cost. In a previous paper [1], a hydromechanical analog of an electronic switch-mode power supply was proposed to create the functional equivalent of a variable displacement pump. This approach combines a fixed displacement pump with a pulse-width-modulated (PWM) on/off valve, a check valve, and an accumulator. The effective pump displacement can be varied by adjusting the PWM duty ratio. Since on/off valves exhibit low loss when fully open or fully closed, the proposed system is potentially more energy efficient than metering valve control, while achieving this efficiency without many of the shortcomings of traditional variable displacement pumps. The system also allows for a host of programmable features that can be implemented via control of the PWM duty ratio. This paper presents initial experimental validation of the concept as well as an investigation of the system efficiency. The experimental apparatus was built using available off-the-shelf components and uses a linear proportional spindle valve as the PWM valve. Experimental results confirm that the proposed approach can achieve variable control function more efficiently than a valve controlled system, and that by increasing the PWM frequency and adding closed-loop control can decrease system response times and of the output ripple magnitude. Sources of inefficiency and their contributions are also investigated via modeling, simulation and are validated by experiments. These indicate design parameters for improving inefficiency.

Download Full-text

An E/H Displacement and Power Control Design for Hydraulic Variable Displacement Pumps

10.1115/imece2001/fpst-25013 ◽

2001 ◽

Author(s):

Hongliu Du

Keyword(s):

Power Control ◽

Mechanical Design ◽

Control Design ◽

Time History ◽

Theoretical Development ◽

Step Response ◽

Displacement Control ◽

Variable Displacement ◽

Error Dynamics ◽

Variable Displacement Pumps

Abstract In this paper, a novel E/H control design is proposed for displacement and power control of hydraulic variable displacement pumps. The displacement control is treated as tracking the desired swashplate angle time history αd(t) with the consideration of system uncertainties. The robust stability of the control system is achieved by a very rugged control design. The resulting error dynamics is of first order, which guarantees no overshoot for step response. An adaptive term is added to further improve the system performance. The smooth transfers between the displacement control and power control modes are achieved. The provided control design significantly simplifies the hydro-mechanical design for variable displacement pumps and results in a cost reduced pump with a better performance. Experimental results validate the theoretical development.

Download Full-text