Power plants – Pressure fluid source and motor – With control means for structure storing work driving energy
Reexamination Certificate
1999-10-04
2002-02-26
Lopez, F. Daniel (Department: 3745)
Power plants
Pressure fluid source and motor
With control means for structure storing work driving energy
C060S419000, C060S465000
Reexamination Certificate
active
06349543
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates primarily to a fluid motor position feedback control system, such as the electrohydraulic or hydromechanical position feedback control system, which includes a fluid motor, a primary variable displacement pump, and a spool-type directional control valve being interposed between the motor and the pump and being modulated by a motor position feedback signal. More generally, this invention relates to the respective fluid motor output feedback control systems and to the respective fluid motor open-loop control systems. In a way of possible applications, this invention relates, in particular, to the hydraulic presses and the motor vehicles. The larger picture of the Energy-Regenerating Adaptive Fluid Control Technology is presented by my several copending US applications including this application and identified also by Ser. Nos. 08/715,470; 08/716,474; 08/715,434; 08/710,323; 08/710,567; 08/725,056.
BACKGROUND ART: TWO MAJOR PROBLEMS
The hydraulic fluid motor is usually driving a variable load. In the variable load environments, the exhaust and supply fluid pressure drops across the directional control valve are changed, which destroys the linearity of a static speed characteristic describing the fluid motor speed versus the valve spool displacement. As a result, a system gain and the related qualities, such the dynamic performance and accuracy, are all the functions of the variable load. Moreover, an energy efficiency of the position feedback control is also a function of the variable load.
The more the load rate and fluctuations, and the higher the performance requirements, the more obvious are the limitations of the conventional fluid motor position feedback control systems. In fact, the heavy loaded hydraulic motor is especially difficult to deal with when several critical performance factors, such as the high speed, accuracy, and energy efficiency, as well as quiet operation, must be combined. A hydraulic press is an impressive example of the heavy loaded hydraulic motor-mechanism. The load conditions are changed substantially within each press circle, including approaching the work, compressing the fluid, the working stroke, decompressing the fluid, and the return stroke. A more comprehensive study of the conventional fluid motor position feedback control systems can be found in numerous prior art patents and publications—see, for example:
a) Johnson, J. E., “Electrohydraulic Servo Systems”, Second Edition. Cleveland, Ohio: Penton /IPC, 1977.
b) Merritt, H. E., “Hydraulic Control Systems”. New York—London—Sydney: John Wiley & Sons, Inc., 1967.
c) Lisniansky, R. M., “Avtomatika e Rugulirovanie Gidravlicheskikh Pressov.” Moscow: Machinostroenie, 1975 (this book had been published in Russian only).
The underlying structural weakness of the conventional fluid motor position feedback control systems can be best characterized by saying that these systems are not adaptive to the changing load environments. The problem of load adaptability of the conventional electrohydraulic and hydromechanical position feedback control systems can be more specifically identified by analyzing two typical hydraulic schematics.
The first typical hydraulic schematic includes a three-way directional control valve in combination with two counteractive (expansible) chambers. The first of these chambers is controlled by said three-way valve which is also connected to the pressure and tank lines of the fluid power means. The second chamber is under a relatively constant pressure provided by said pressure line. In this case, it is not possible to automatically maintain a supply fluid pressure drop across the three-way valve without a “schematic operation interference” with the position feedback control system. Indeed, maintaining the supply fluid pressure drop can be achieved only by changing the pressure line pressure, which is also applied to the second chamber and, therefore, must be kept approximately constant.
The second typical schematic includes a four-way directional control valve in combination with two counteractive chambers. Both of these chambers are controlled by the four-way valve which is also connected to the pressure and tank lines of the fluid power means. In this schematic, it is not possible to automatically maintain an exhaust fluid pressure drop across the four-way valve without encountering the complications which can also be viewed as a schematic operation interference with the position feedback control system. Indeed, a chamber's pressure signal which is needed for maintaining the exhaust fluid pressure drop, must be switched over from one chamber to the other in exact accordance with a valve spool transition through a neutral spool position, where the chamber lines are switched over, to avoid damaging the spool valve flow characteristics. In addition, a pressure differential between the two chambers at the neutral spool position will affect the pressure drop regulation and may generate the dynamic instability of the position feedback control system.
The problem of load adaptability can be still further identified by emphasizing a possible dynamic operation interference between the position feedback control and the regulation of the exhaust and supply fluid pressure drops.
The problem of load adaptability can be still further identified by emphasizing a possible pressure drop regulation interference between the supply and exhaust line pressure drop feedback pressure systems.
The structural weakness of the conventional fluid motor position feedback control systems can be still further characterized by that these systems are not equipped for regenerating a load related energy, such as a kinetic energy of a load mass or a compressed fluid energy of the fluid motor-cylinder. As a result, this load related energy is normally lost. The problem of load adaptive regeneration of energy is actually correlated with the problem of load adaptability of the fluid motor position feedback control system, as it will be illustrated later.
Speaking in general, the problem of load adaptability and the problem of load adaptive regeneration of energy are two major and interconnected problems which are to be solved consecutively by this invention, in order to create a regenerative adaptive fluid motor position feedback control system, and finally, in order to create a regenerative adaptive fluid motor output feedback control system and a regenerative adaptive fluid motor open-loop control system.
SUMMARY OF THE INVENTION
The present invention is primarily aimed to improve the performance qualities and energy efficiency of the fluid motor position feedback control system, such as the electrohydraulic or hydromechanical position feedback control system, operating usually in the variable load environments. The improvement of performance qualities, such as the dynamic performance and accuracy, is the first concern of this invention, while the improvement of energy efficiency is the second but closely related concern.
This principal object is achieved by:
a) shaping and typically linearizing the flow characteristics of the directional control valve by regulating the supply and exhaust fluid pressure drops across this valve;
b) regulating the hydraulic fluid power delivered to the directional control valve, in accordance with, but above, what is required by the fluid motor;
c) preventing a schematic operational interference between the regulation of said pressure drops and the position feedback control;
d) preventing a dynamic operation interference between the regulation of said pressure drops and the position feedback control (as it will be explained later);
e) preventing a pressure drop regulation interference between the supply and exhaust line pressure drop feedback control systems (as it also will be explained later).
The implementation of these interrelated steps and conditions is a way of transition from the conventional fluid motor position feedback control systems to the load adaptive fluid motor position feedback control systems. These load a
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