Initial pressure governor for a variable displacement pump

Details Initial pressure governor for a variable displacement pump Initial pressure governor for a variable displacement pump

1994-06-10

1996-12-24

Freay, Charles G.

Pumps

Condition responsive control of drive transmission or pump...

Adjustable cam or linkage

60452, F04B 4902

Patent

active

055868690

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The invention relates to an initial pressure governor for a variable displacement pump, in particular to a main pump working at a high initial pressure level of a compression unit for a hydraulic driving unit, e.g. the driving cylinder(s) of a thick matter pump.


BACKGROUND OF THE INVENTION

A pressure governor is provided with a pump capacity regulator which is controllable by means of a hydraulic motor operator which can be driven by alternative pressurization and depressurization of a driving chamber for carrying out the movements for the opposite changes of the displaced volume of the variable displacement pump. Typically a pressure regulated valve is designed for controlling the pressurization and depressurization of this pressure driving chamber, which, regulated by the initial pressure of the pump or a pressure proportional to this, from a minimum pressure determined by a minimum restoring force of a restoring element, e.g. a spring, releases an initial pressure together with the control pressure coupled into its control chamber, by which the driving pressure chamber of the motor operator is pressurized.
Such pressure governors are well known. They comprise a valve driven by the initial pressure of the variable displacement pump designed, for example, as a proportional valve which, with increasing initial pressure of the variable displacement pump, is increasingly pushed against the restoring force of a valve spring into the functional position providing the activation of the actuating drive, whereby in the stationary position of the pressure control the initial pressure of the variable displacement pump is determined by the preset initial tension of the valve spring. This type of control which may be superimposed by a volume flow control, which--on a lower pressure level than the maximum level determined by the pressure regulating valve--provides a constant control of the volume flow of the high-pressure pump. It has, however, the disadvantage that in the starting situations of a hydraulic power consumer which, in the stationary position of its movements, needs a relatively high operating pressure level. Thus, strong pressure shocks may occur which promote wear and are combined with considerable noise, because in the starting situation the pressure governor is adjusted to a maximum capacity volume of the variable displacement pump which is reduced only after pumping starts. Comparable with this is also the situation that the consumer or a driving cylinder thereof is blocked, because then also the initial pressure of the variable displacement pump increases very fast--like a shock--to the value given by the pressure limit. These problems are particularly aggravating with hydraulic power consumers which are driven by linear cylinders or hydraulic oscillating motors carrying out periodic oscillating movements.


SUMMARY OF THE INVENTION

The object of the invention is to improve a control unit of the type described at the beginning in such a manner that, in particular in starting situations of a hydraulic consumer a gentle increase of the operating pressure is obtained and/or with load changes such as a sudden increase of the load a correspondingly gentle increase of the operating pressure to a given maximum value is obtained.
According to the invention, a restoring element is set to a restoring force which corresponds only to a small fraction of e.g. 1/50 to 1/10 of the control force which can be maximally generated and which acts on the valve piston of the proportional valve in that the pressure regulated valve is provided with a restoring chamber as a second control chamber, by the pressurization of which a restoring force opposite to the control force can be generated, the maximum value of which corresponds at least approximately to that of the control force, and in that the pressure coupled into the restoring chamber is derived by means of a hydraulic retarder by the pressure coupled into the control chamber of the pressure regulated valve.
Accordingly, when the hydraulic

REFERENCES:
patent: 5173031 (1992-12-01), Nonnenmacher et al.

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