Positive-displacement machine

Abstract

A hydraulic positive-displacement machine includes at least two radially or axially spaced-apart groups of cylinder-piston units. The cylinders of the primary group can be made to communicate fluidically with cylinders of the secondary group via intermediate valves. At least two intermediate valves can be switched independently of one another.

Description

BACKGROUND OF THE INVENTION[0001]The invention relates to a hydraulic positive-displacement machine.[0002]In conventional hydrostatic positive-displacement machines, which can be embodied as radial or axial piston machines, for instance, the control of the inflow and outflow of the individual cylinder-piston units revolving along an orbit is done mechanically. In the case of an axial piston pump, for example, two pressure crescents are used, by way of which the connections with the high-pressure side and the low-pressure side open during a certain range of the orbit and thus during a certain stroke segment of the cylinder-piston units.[0003]In radial piston pumps, one high-pressure valve and one low-pressure valve per cylinder-piston unit are provided, and the valves are, mechanically controlled. The high-pressure valve of each unit for instance always opens if a certain built-up pressure in the applicable cylinder of the unit is exceeded, so that the pressure fluid with elevated pr...

AI Technical Summary

Benefits of technology

[0011]The hydraulic positive-displacement machine according to the invention has at least two groups, spaced apart radially or axially from one another, of cylinder-piston units, in which cylinders of the primary group can be made to communicate fluidically with cylinders of the secondary group via intermediate valves. According to the invention, at least two intermediate valves are switchable independently of one another. As a result, the flexibility of the volumetric flow (in the case of a pump) or torque (In the case of a motor) is increased.

[0024]In a preferred refinement of the positive-displacement machine of the invention, the secondary cylinder-piston units have a larger idle volume than the primary cylinder-piston units. Thus the “relative expansion” of the pressure fluid in the shut-off state of the secondary cylinder-piston units upon the outward motion of their pistons is reduced, thus reducing the lost energy of the machine in that operating state.

Problems solved by technology

A disadvantage of such hydrostatic positive-displacement machines is that all the cylinder-piston units are always active, or in other words that the volume flow of the machine is always defined by the displacement of all the units.

A disadvantage of such valve-controlled positive-displacement machines is that the cylinder-piston units switched to be forceless in the idle mode also have pressure fluid flowing through them, resulting in a friction loss.

A disadvantage of such positive-displacement machines is that the cylinder-piston units of the second radial plane can be switched on or off only in common.

Images