A variable displacement pump is a device that converts

mechanical energy In physical sciences, mechanical energy is the sum of potential energy and kinetic energy. The principle of conservation of mechanical energy states that if an isolated system is subject only to conservative forces, then the mechanical energy is ...

to hydraulic (fluid) energy. The displacement, or amount of fluid pumped ''per revolution of the pump's input shaft'' can be varied while the pump is running. Many variable displacement pumps are "reversible", meaning that they can act as a hydraulic motor and convert fluid energy into mechanical energy.

Types

A common variable displacement pump used in vehicle technology is the

axial piston pump An axial piston pump is a positive displacement pump that has a number of pistons in a circular array within a ''cylinder block''. It can be used as a stand-alone pump, a hydraulic motor or an automotive air conditioning compressor. Description ...

. This pump has several

piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas- ...

s in

cylinder A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infi ...

s arranged parallel to each other and rotating around a central shaft. A

swashplate A swashplate, also known as slant disk, was invented by Anthony Michell in 1917. It is a mechanical engineering device used to translate the motion of a rotating shaft into reciprocating motion, or vice versa. The working principle is similar to ...

at one end is connected to the pistons. As the pistons rotate, the angle of the plate causes them to move in and out of their cylinders. A rotary valve at the opposite end from the swashplate alternately connects each cylinder to the fluid supply and delivery lines. By changing the angle of the swashplate, the stroke of the pistons can be varied continuously. If the swashplate is perpendicular to the axis of rotation, no fluid will flow. If it is at a sharp angle, a large volume of fluid will be pumped. Some pumps allow the swashplate to be moved in both directions from the zero position, pumping fluid in either direction without reversing the rotation of the pump. An efficient variation is the bent axis pump. Bending the axis reduces side loads on the pistons. Piston pumps can be made variable-displacement by inserting springs inline with the pistons. The displacement is not positively controlled, but decreases as back-pressure increases. Another variation is the variable displacement vane pump.

External links

Principle of a variable displacement pump (Video)
{{DEFAULTSORT:Variable Displacement Pump Pumps