Power plants – Pressure fluid source and motor – Methods of operation
Patent
1998-08-04
2000-11-14
Lopez, F. Daniel
Power plants
Pressure fluid source and motor
Methods of operation
60414, 91519, F15B 1033, F15B 11036
Patent
active
061453072
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for controlling a multistage hydraulic cylinder of an implement, that acts on a load, including at least two selectively connectable active areas and being supplied with hydraulic fluid via a hydraulic pump, a hydraulic accumulator and a control valve. The invention also relates to a hydraulic system for an implement, the system including a hydraulic cylinder to which hydraulic fluid is suppliable from a hydraulic accumulator and/or a hydromotor via a control valve for advancing, holding or retracting a piston, wherein the hydraulic cylinder includes several active areas that are selectively controllable for actuating the hydraulic cylinder.
Apart from the hydromotor, hydraulic cylinders are indispensable devices in modern hydraulic installations for transforming hydraulic energy into mechanical energy. In a hydraulic installation, a hydromotor is commonly driven by a motor, and hydraulic fluid is sucked from a tank and conveyed through the pressure line of the hydraulic installation toward the hydraulic cylinder. Via a distributing valve in the pressure line between hydromotor and hydraulic cylinder, the direction of displacement of the piston in the hydraulic cylizider can be controlled. The hydraulic cylinder to which a load is applied constitutes a resistance for the hydraulic fluid, with the pressure in the hydraulic cylinder rising until the resulting force is sufficient to displace the piston against the resistance of the load. The maximum movable force is essentially predetermined by the maximum pump pressure and the effective diameter of the hydraulic cylinder.
The maximum displacemnent velocity of the piston of the hydraulic cylinder depends on the maximum conveyed flow of the hydromotor. For the case that speedy actuating movements of the hydraulic cylinder are required, a high pump performance must be provided. In order to keep the pump performance requirements low, there is provided in the pressure line a hydraulic accumulator which is filled by the pump when, during a work cycle, the volume flow required for advancing the hydraulic cylinder is smaller than the maximum pump volume flow. If in an operating condition the maximum volume flow is required for speedily advancing the hydraulic cylinder, then the difference with the volume flow of the pump may be taken from the hydraulic accumulator. Use of these hydraulic accumulators thus permits to reduce the maximum pump performance. Upon retraction of the hydraulic cylinder, the displaced hydraulic fluid is again conveyed back into the tank, in which case heating occurs owing to throttling of the returning hydraulic fluid. The energy stored in the returning hydraulic fluid is lost practically unused. Inasmuch as constant efforts are directed at minimising energy expenditure as far as possible in modern hydraulic installations, solutions have been proposed wherein the hydraulic pump is designed such as to act, upon retraction of the hydraulic cylinder, as a motor which is driven by the returning hydraulic fluid. Through this hydromotor it is possible e.g. to drive a generator, such that part of the energy stored in the returning hydraulic fluid is transformed into mechanical or electrical energy. Undesirable heating of the hydraulic fluid is moreover prevented as the latter need not be throttled any more.
Owing to the particular configuration of the hydraulic pump, this solution does, however, require considerable expense in terms of device technology and thus increased investment costs.
In contrast, the invention is based on the object of creating a method for controlling a hydraulic cylinder and a hydraulic installation of a utility vehicle, which permit operation of the utility vehicle at minimised energy consumption yet minimum expense in terms of device technology.
This object is achieved by the features of the invention as described below.
Owing to the measure of providing a hydraulic cylinder with a plurality of effective areas and controlling these effective areas of the hydraulic cylinder in dependence on
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Lopez F. Daniel
Mannesman Rexoth AG
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