Source: http://www.google.com/patents/US5794441?dq=5,838,906
Timestamp: 2016-07-31 03:46:56
Document Index: 697317149

Matched Legal Cases: ['art 21', 'art 21', 'art 21', 'art 21', 'art 21', 'art 21', 'Art.\n11']

Patent US5794441 - Adaptive fluid feedback control - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inPatentsA regenerative adaptive fluid motor position feedback control system integrating a load adaptive flujid motor position feedback system having an energy accumulator. the fluid motor control system includes a primary variable displacement pump powering a spool valve controlling a fluid motor accumulating...http://www.google.com/patents/US5794441?utm_source=gb-gplus-sharePatent US5794441 - Adaptive fluid feedback controlAdvanced Patent SearchPublication numberUS5794441 APublication typeGrantApplication numberUS 08/710,567Publication dateAug 18, 1998Filing dateSep 19, 1996Priority dateNov 5, 1981Fee statusLapsedPublication number08710567, 710567, US 5794441 A, US 5794441A, US-A-5794441, US5794441 A, US5794441AInventorsRobert Moshe LisnianskyOriginal AssigneeLisniansky; Robert MosheExport CitationBiBTeX, EndNote, RefManPatent Citations (8), Referenced by (11), Classifications (51), Legal Events (8) External Links: USPTO, USPTO Assignment, EspacenetAdaptive fluid feedback control
US 5794441 AAbstract
A regenerative adaptive fluid motor position feedback control system integrating a load adaptive flujid motor position feedback system having an energy accumulator. the fluid motor control system includes a primary variable displacement pump powering a spool valve controlling a fluid motor accumulating a load related energy, such as a kinetic energy of a mass load of the fluid motor or a compressed fluid energy of the fluid motor-cylinder. The load related energy of the fluid motor is regenerated to provide a load adaptive exchange of energy between the fluid motor and the energy accumulator. This load adaptive exchange of energy is combined with a load adaptive primary energy supply for maximizing the over-all energy efficiency and performance potentials of the fluid motor control. The load adaptability is achieved by regulating the exhaust and supply fluid pressure drops across the spool valve. The regenerative adaptive fluid motor control can be used, for example, for constructing the high energy-efficient, load adaptive motor vehicles and the high energy-efficient, load adaptive hydraulic presses.
1. A regenerative adaptive fluid motor position feedback control method comprising the steps of:constructing a fluid motor position feedback control system including fluid motor and load means, spool valve means, fluid power means, and position feedback control means; said fluid motor and load means including a fluid motor means and motor load means and accumulating a load related energy; said spool valve means having at least three fluid power lines including a motor line conducting a motor fluid flow to or a motor fluid flow from said fluid motor means of said fluid motor and load means, a power supply line, and a separate exhaust power line conducting only said motor fluid flow from said fluid motor means of said fluid motor and load means; said fluid power means including a variable delivery fluid power supply generating a pressurized fluid stream being implemented for powering said supply power line of said spool valve means; said position feedback control means measuring a motor position of said fluid motor means and producing a position feedback control error signal; regulating said motor position of said fluid motor means by said fluid motor position feedback control system by modulating said spool valve means by said position feedback control error signal; introducing an exhaust line energy recuperating means for varying a counterpressure rate in said separate exhaust power line and for recuperating said load related energy of said fluid motor and load means; constructing an energy recuperating pressure drop feedback control system including said exhaust line energy recuperating means; regulating an exhaust fluid pressure drop across said spool valve means by said energy recuperating pressure drop feedback control system by varying said counterpressure rate in said separate exhaust power line by said exhaust line energy recuperating means; preventing a substantial dynamic operation interference between regulating said exhaust fluid pressure drop and regulating said motor position by providing a significant dynamic performance superiority for said energy recuperating pressure drop feedback control system against said fluid motor position feedback control system by providing either a significant frequency-response superiority or a significant final-transient-time superiority for said energy recuperating pressure drop feedback control system against said fluid motor position feedback control system; constructing a load adaptive energy recuperating system including load adaptive energy converting means and energy accumulating means; said load adaptive energy converting means including said energy recuperating pressure drop feedback control system; providing a load adaptive recuperation of said load related energy of said fluid motor and load means by said load adaptive energy recuperating system by converting said load related energy through said load adaptive energy converting means including said energy recuperating pressure drop feedback control system to a recuperated energy of said energy accumulating means for storing and subsequent use of said recuperated energy; facilitating said load adaptive recuperation of said load related energy of said fluid motor and load means by regulating said exhaust fluid pressure drop across said spool valve means by said energy recuperating pressure drop feedback control system; constructing a supply line pressure drop feedback control system including said variable delivery fluid power supply; regulating a supply fluid pressure drop across said spool valve means by said supply line pressure drop feedback control system by varying a pressure rate of said pressurized fluid stream by a variable delivery means of said variable delivery fluid power supply; preventing a substantial dynamic operation interference between regulating said supply fluid pressure drop and regulating said motor position by providing a significant dynamic performance superiority for said supply line pressure drop feedback control system by providing either a significant frequency-response superiority or a significant final-transient-time superiority for said supply line pressure drop feedback control system against said fluid motor position feedback control system. 2. The method according to claim 1, wherein said exhaust line energy recuperating means includes an exhaust line variable displacement motor being powered by said separate exhaust power line, and wherein varying said counterpressure rate in said separate exhaust power line is accomplished by an exhaust line variable displacement means of said exhaust line variable displacement motor.
3. The method according to claim 1, wherein said exhaust line energy recuperating means includes an exhaust line fluid motor being powered by said separate exhaust power line and driving an exhaust line variable displacement pump, and wherein varying said counterpressure rate in said separate exhaust power line is accomplished by an exhaust line variable displacement means of said exhaust line variable displacement pump.
4. The method according to claim 1, wherein said fluid motor means includes at least one hydraulic cylinder having at least one loadable chamber, and wherein said load related energy of said fluid motor and load means includes a compressed fluid energy of said loadable chamber of said hydraulic cylinder.
5. The method according to claim 1, wherein said motor load means include a frame of a hydraulic press, wherein said fluid motor means include at least one hydraulic cylinder of said hydraulic press, wherein said hydraulic cylinder includes a loadable chamber being loaded against said frame of said hydraulic press, and wherein said load related energy of said fluid motor and load means includes a compressed fluid energy of said loadable chamber of said hydraulic cylinder of said hydraulic press.
6. The method according to claim 1, wherein said motor load means include a mass load of said fluid motor means, and wherein said load related energy of said fluid motor and load means includes a mechanical energy of a mass of said mass load.
7. The method according to claim 1, wherein said motor load means include a mass of a wheeled vehicle, wherein said fluid motor means are loaded by said mass of said wheeled vehicle, and wherein said load related energy of said fluid motor and load means includes a mechanical energy of said mass of said wheeled vehicle.
8. The method according to claim 1, wherein said variable delivery fluid power supply includes a variable displacement pump generating said pressurized fluid stream, and wherein varying said pressure rate of said pressurized fluid stream is accomplished by a variable displacement means of said variable displacement pump.
9. The method according to claim 1, wherein said variable delivery fluid power supply includes a variable speed motor driving a fluid pump generating said pressurized fluid stream, and wherein varying said pressure rate of said pressurized fluid stream is accomplished by said variable speed motor.
10. A regenerative adaptive fluid motor position feedback control system comprising:a fluid motor position feedback control system including fluid motor and load means, spool valve means, fluid power means, and position feedback control means; said fluid motor and load means including fluid motor means and motor load means and accumulating a load related energy; said spool valve means having at least three fluid power lines including a motor line conducting a motor fluid flow to or a motor fluid flow from said fluid motor means of said fluid motor and load means, a supply power line, and a separate exhaust power line conducting only said motor fluid flow from said fluid motor means of said fluid motor and load means; said fluid power means including a variable delivery fluid power supply generating a pressurized fluid stream being implemented for powering said power supply line of said spool valve means; said position feedback control means measuring a motor position of said fluid motor means and producing a position feedback control error signal being implemented for modulating said spool valve means; an exhaust line energy recuperating means including an exhaust line fluid motor for varying a counterpressure rate in said separate exhaust power line and for recuperating said load related energy of said fluid motor and load means; an energy recuperating pressure drop feedback control system including said exhaust line energy recuperating means and operable to regulate an exhaust fluid pressure drop across said spool valve means by varying said counterpressure rate in said separate exhaust power line by said exhaust line energy recuperating means; said energy recuperating pressure drop feedback control system having a significant dynamic performance superiority against said fluid motor position feedback control system by having either a significant frequency-response superiority or a significant final-transient-time superiority against said fluid motor position feedback control system; a load adaptive energy recuperating system including load adaptive energy converting means and energy accumulating means; said load adaptive energy converting means including said energy recuperating pressure drop feedback control system and operable to convert said load related energy of said fluid motor and load means to a recuperated energy of said energy accumulating means for storing and subsequent use of said recuperated energy; a supply line pressure drop feedback control system including said variable delivery fluid power supply and operable to regulate a supply fluid pressure drop across said spool valve means by varying a pressure rate of said pressurized fluid stream by a variable delivery means of said variable delivery fluid power supply; said supply line pressure drop feedback control system having a significant dynamic performance superiority against said fluid motor position feedback control system by having either a significant frequency-response superiority or a significant final-transient-time superiority against said fluid motor position feedback control system. 11. A regenerative adaptive press drive system comprising:a fluid motor position feedback control system including fluid motor and load means, spool valve means, fluid power means, and position feedback control means; said fluid motor and load means including fluid motor means of a hydraulic press and accumulating a compressed fluid energy of said fluid motor means of said hydraulic press; said spool valve means having at least three fluid power lines including a motor line conducting a motor fluid flow to or a motor fluid flow from said fluid motor means of said hydraulic press, a supply power line, and a separate exhaust power line conducting only said motor fluid flow from said fluid motor means of said hydraulic press; said fluid power means including a variable delivery fluid power supply generating a pressurized fluid stream being implemented for powering said supply power line of said spool valve means; said position feedback control means measuring a motor position of said fluid motor means and producing a position feedback control error signal being implemented for modulating said spool valve means; an exhaust line energy recuperating means for varying a counterpressure rate in said separate exhaust power line and for recuperating said compressed fluid energy of said fluid motor means of said hydraulic press; an energy recuperating pressure drop feedback control system including said exhaust line energy recuperating means and operable to regulate an exhaust fluid pressure drop across said spool vale means by varying said counterpressure rate in said separate exhaust power line by said exhaust line energy recuperating means; said energy recuperating pressure drop feedback control system having a significant dynamic performance superiority against said fluid motor position feedback control system by having either a significant frequency-response superiority or a significant final-transient-time superiority against said fluid motor position feedback control system; a load adaptive energy recuperating system including load adaptive energy converting means and energy accumulating means; said load adaptive energy converting means including said energy recuperating pressure drop feedback control system and operable to convert said compressed fluid energy of said fluid motor means of said hydraulic press to a recuperated energy of said energy accumulating means for storing and subsequent use of said recuperated energy; a supply line pressure drop feedback control system including said variable delivery fluid power supply and operable to regulate a supply fluid pressure drop across said spool valve means by varying a pressure rate of said pressurized fluid stream by a variable delivery means of said variable delivery fluid power supply; said supply line pressure drop feedback control system having a significant dynamic performance superiority against said fluid motor position feedback control system by having either a significant frequency-response superiority or a significant final-transient-time superiority against said fluid motor position feedback control system. 12. The drive system according to claim 11, wherein said fluid motor means includes at least one hydraulic cylinder having a loadable chamber being loaded against a frame of said hydraulic press, and wherein said compressed fluid energy of said fluid motor means of said hydraulic press includes a compressed fluid energy of said loadable chamber of said hydraulic cylinder of said hydraulic press.
This is a continuation-in-part of application Ser. No. 08/400,617, filed Mar. 8, 1995, now abandoned which is a continuation-in-part of application Ser. No. 08/075,288, filed Jun. 11, 1993, now abandoned, which is a continuation-in-part of application Ser. No. 07/815,175, filed Dec. 31, 1991, now abandoned, which is a continuation-in-part of application Ser. No. 07/521,663, filed May 10, 1990, now abandoned, which is a continuation-in-part of application Ser. No. 07/096,120, filed Sep. 14, 1987, now abandoned, which is a divisional of application Ser. No. 06/737,063, filed May 23, 1985, now abandoned, which is a continuation-in-part of application Ser. No. 06/704,325filed Feb. 13, 1985, now abandoned, which is a continuation-in-part of application Ser. No. 06/318,672, filed Nov. 5, 1981, now abandoned.
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.
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 as the dynamic performance and accuracy, are all the functions 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. Clevelang, 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 Regulirovanie Gidravlicheskikh Pressov". Moscow: Mashinostroenie, 1975 (this book had been published in Russian only).
The second typical schematic includes a four-way directional control valve in combination with the 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 ve 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 unstability 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 reulation of the exahaust and supply fluid pressure drops.
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.
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.
In a case when only one of two counteractive chambers of the fluid motor is controllable, the fluid motor can be loaded only in one direction. The controlled chamber is connected to the three-way spool valve which also has a supply power line and an exhaust power line. In this case, the second chamber is under a relatively constant pressure supplied by an independent source of sluid power.
Using the three-way or five-way spooln valve with a separate exhaust line for each controllable chamber, makes it possible to prevent a schematic operation interference between the position feedback control and the regulation of pressure drops. In particular, the problem of measuring a chamber's pressure signal is eliminated. Each counterpressure line is provided with an exhaust line pressure drop regulator, which is modulated by an exhaust line pressure drop feedback signal which is measured between this counterpressure line and the related chamber.
In the process of maintaining the exhaust fluid pressure drop across the spool valve, all the flow is being released from the counterpressure line through the exhaust line pressure created in the counterpressure line only for a short time while the hydraulic fluid in the preloaded chamber is being decompressed. However, the control over the decompression is critically important for improving the system's dynamic performance potential.
A family of load adaptive fluid position servomechanisms may include the three-, four-, five-, and six-way directional valves. The three-way spool valve is used to provide the individual pressure and counterpressure lines for only one controllable chamber. The six-way spool valve is used to proved the separate supply and exhaust lines for each of two controllable chambers. The five-way spool valve can be derived from the six-way spool valve by connecting together two separate supply lines. The four-way spool valve can be derived from the five-way spool valve by connecting together two separate exhaust lines. The four-way spool valve does create a problem of schematic operation interference between the position feedback control and the regulation of pressure drops, as it is already explained above. However, the principal possibility of using the four-way spool valve in the adaptive position servomechanisms is not excluded.
What is in common for the adaptive fluid position servomechanisms being considered is that the fluid motor is provided with at least one controlled and loadable chamber, and that this chamber is provided with the pressure-compensated spool valve flow characteristics. These pressure-compensated flow characteristics are shaped by the related exhaust line pressure drop feedback control system which includes the exhaust line pressure drop regulator and by the related supply line pressure drop feedback control system which includes the primary variable displacement pump.
(1) The supply and exhaust line pressure drop command signals are set approximately constant for linearizing the pressure-compensated spool valve flow characteristics. The related adaptive hydraulic (electrohydraulic or hydromechanical) position servomechanismsc can be referred to as the linear adaptive servomechanisms, or as the fully-compensated adaptive servomechanisms. Still other method of programming the pressure drop command signals can be specified with respect to the linear adaptive servomechanisms, as it is illustrated below--by points 2 to 5.
(3) The supply line pressure drop command signal is being reduced slightly as the respective load pressure rate is increased, so that to provide at least some under-compensation along the exhaust power line.
It is further object of this invention to develop a concept of load adaptive regeneration of a load related energy, such as a kinetic energy of a load mass or a compressed fluid energy of the fluid motor-cylinder. This is achieved by replacing the exhaust line pressure drop regulator by a counterpressure varying and energy recupturing means (such as an exhaust line variable displacement motor or an exhaust line constant displacement motor driving an exhaust line variable displacement pump), by replacing the exhaust line pressure drop feedback control system by an energy recupturing pressure drop feedback control system, and finally, by creating a load adaptive energy regenerating system including fluid motor and load means and energy accumulating means.
It is still further object of this inventiion to develop a concept of load adaptive exchange of energy between the fluid motor and load means and the energy accumulating means of the load adaptive energy regenerating system. The load adaptive regeneration of the load related energy of the fluid motor and load means can be viewed as a part (or as a larger part) of a complete circle of the load adaptive exchange of energy between the fluid motor and load means and the energy accumulating means.
It is still further object of this invention to develop a regenerative adaptive fluid motor output feedback control system and a regnerative adaptive fluid motor open-loop control system. In general, the regenerative adaptive fluid control makes it possible to combine the load adaptive primary power supply and the load adaptive regeneration of energy for maximizing the over-all energy efficiency and performance potentials of the fluid motor control systems.
Further objects, advantages, and futures of this invention will be apparent from the following detailed description when read in conjunction with the drawings.
FIG. 1 shows the adaptive fluid servomechanism having only one controllable chamber.
FIG. 15 shows a generalized modes of the regenerative adaptive fluid motor open-loop control systems.
FIG. 29 swhows a generalized regenerative system having a supplementary output motor.
GENERAL LAYOUT AND THEORY
Introduction: Adaptive fluid position feedback control.
The schematic of FIG. 1 further includes the hydraulic power supply means 3-1 having a primary variable displacement pump powering the pressure line 51. The three-way spool-type hydraulic power lines including a motor line--line L1--connected to line 15 of chamber 10, the supply power line L2 connected to pressure line 51, and the exhaust power line L3. Lines L2 and L3 are commutated with line L1 by the spool valve 2. To consider all the picture, FIG. 1 should be studied together with the related-supplementary FIGS. 2, 3-A, and 3-B.
The block 4 represents a generalized model of the optional position feedback control means. This bloc is needed to actually make-up the fluid motor position feedback control system, which is capable of regulating the motor position X1 of motor 1 by employing the motor position feedback signal CXl, where coefficient "C" is, usually, constant. The motor position feedback signal CXl is generated by a motor position sensor, which is included into block 4 and is connected to the moving part 21 of the hydraulic fluid motor 1.
An original position feedback control error signal ΔXor is produced as a difference between the position input-command signal Xo and the motor position feedback signal CXl. There are at least two typical fluid motor position feedback control systems--the electrohydraulic and hydromechanical position feedback control systems. In the electrohydraulic system, the equation
&#916;Xor =Xo -CXl or the like is simulated by electrical means located within block 4. In the hydrochemical system, the equation
&#916;Xor =Xo -CXl or the like is simulated by mechanical means located within block 4.
The block 4 may also include the electrical and hydraulic amplifiers, an electrical torque motor, the stabilization--optimization technique and other components to properly amplify and condition said signal ΔXor for modulating said valve 2. In other words, the original position feedback control error signal ΔXor is finally translated into a manipulted position feedback control error signal ΔX which can be identified with the valve spool displacement ΔX from the neutral spool position ΔX=0.
In general, it can be said that the manipulated position feedback control error signal ΔX is derived in accordance with a difference between the position input-command signal Xo and the output position signal Xl. At the balance of the position feedback control:
&#916;Xor =Xo -CXl &#8773;0
and, hence ΔX≅0. On the other hand and for simplicity, it can also be often assumed that
&#916;&#8773;Xo -CXl This principal characterization of the optional position feedback control means is, in fact, well known in the prior art and will be extended to still further details later.
The exhaust line pressure drop regulator 3-3 is introduced to make up the exhaust line pressure drop feedback control system which is capable of regulating the exhaust fluid pressure drop across valve 2 by varying the counterpressure rate P3 in the exhaust power line L3. This exhaust line pressure drop feedback signal, which is equal P03 -P3 and is measured between the exhaust power line L3 and the related exhaust signal line SL3 connected to line L1. The regulator 3-3 is connected to the exhaust power line L3 and to the tank line 52 and is modulated by an exhaust line pressure drop feedback control error signal, which is produced in accordance with a difference between the exhaust line pressure drop command signal ΔP3 and the exhaust line pressure drop feedback signal P03 -P3.
The primary variable displacement pump of fluid power supply means 3-1 (pump 58 on FIG. 2) is introduced to make-up the supply line pressure drop feedback control system, which is capable of regulating the supply fluid pressure drop across valve 2 by varying the pressure rate P2 in the supply power line L2 by varying the supply fluid flow rate in said line L2 by said variable displacement pump. This supply fluid pressure drop is represented by the supply line pressure drop feedback signal, which is equal P2 -P02 and is measured between line L2 (through line 32 on FIG. 2) and the related supply signal line SL2 connected to line L1. A variable delivery means 56 of pump 58 is modulated by a supply line pressure drop feedback control error signal, which is produced in accordance with a difference between the supply line pressure drop command signal ΔP2 and the supply line pressure feedback signal P2 -P02.
The schematic shown on FIG. 1 operates as follows. At the balance of the motor position feedback control:
&#916;X&#8773;Xo -CXl =0.
When the hydraulic fluid motor 1 is moving from the one position Xl to the other, the motor speed is defined by the valve spool displacement
&#916;X&#8773;Xo -CXl from the neutral spool position ΔX=0. The system performance potential is substantially improved by providing the linearity of the spool valve flow characteristic
F=Kl &#916;X,
where Kl is the constant coefficient, and F is the fluid flow rate to (Fin) or the fluid flow rate from (Fout) the controllable chamber 10. this linearity is achieved by applying the supply line pressure drop command signal ΔP2 =constant to the supply line pressure drop feedback control system and the exhaust line pressure drop feedback control system, respectively.
the pressure maintained in the supply power line L2 by the supply line pressure drop feedback control system is
P2 =P02 +&#916;P2 and can be just slightly above what is required for chamber 10 to overcome the load. On the other hand, the counterpressure maintained in the exhaust power line L3 by the exhaust line pressure drop feedback control system is
P3 =P03 -&#916;P3 and can be just slightly below the pressure P03 =P02 in chamber 10. However, there are some limits for acceptable reduction of the pressure drop command signals ΔP2 and ΔP3.
The pressure drop command signals ΔP2 and ΔP3, the pressure P0 and their interrelationship are selected for linearising the spool valve flow characteristic
(F=Kl &#916;X)
without "running a risk" of full decompressing the hydraulic motor (chamber 10) and generating the hydraulic shocks in the hydraulic system. Some of the related considerations are:
1. The pressure P0 has to compress the hydraulic fluid in chamber 10 to such an extent as to prevent the full decompression under the dynamic operation conditions. In the absence of static and dynamic loading, the pressure P10 in chamber 10 is fixed by the pressure P0 applied to chamber 11 so that
P10 =Ko P0,
where Ko is the constant coefficient.
2. The pressure drop command signal ΔP3 is selected as:
&#916;P3 =P10 =Ko P0.
Under this condition, the pressure drop
P03 -P3 =&#916;P3 can be maintained even during the return stroke. Indeed, after decompressing the preloaded chamber 10, the regulator 3-3 is open (P3 =0), but the pressure drop
P03 -0=&#916;P3 =Ko P0 is still maintained simply by approximately constant pressure P0.
3. If the passages of the spool valve 2 are symmetrical relative to the point ΔX=0, the pressure drop command signals ΔP2 and ΔP3 are to be approximately equal. In this case: ##EQU1## where: P2min is the minimum pressure rate maintained in line L2 by the supply line pressure drop feedback control system.
4. The smaller pressure drop command signals ΔP2 and ΔP3, the larger spool valve 2 is required to conduct the given fluid flow rate.
The regulator 3-3 is opened by a force of the spring shown on FIG. 1 and is being closed to provide the counterpressure P3 only after the actual pressure drop P03 -P3 exceeds its preinstalled value ΔP3, which is defined by the spring force. Practically, at the very beginning of the return stroke, when the regulator 3-3 has to enter into the operation, the controllable chamber 10 is still under the pressure. It means that regulator 3-3 is preliminarily closed and is maintained by regulator 3-3 only for a short time of decompressing chamber 10. However, the control over the decompression is critically important for improving the system's dynamic performance potential.
The schematic of FIG. 2 is a disclosure of block 3-1 shown on FIG. 1. this schematic includes the primary variable displacement pump 58, which is connected through line 30 and check valve 44 to the pressure line 51. A relatively low pressure, high capacity fluid power supply 50 (such as a centrifugal pump) is also connected through line 54 and check valve 40 to the pressure line 51. The primary motors (such as electrical motors) driving the pumps are not shown in FIG. 2. The variable displacement mechanism of this pump. The tank lines 52 and 36 are collected by the oil tank 62. The pressure line 51 can be protected by the maximum pressure relief valve which is not shown on FIG. 2. The maximum pressure in line 51 can also be restricted by using the variable delivery means 56 of pump 58. In general, the maximum pressure relief valves can also be used to protect other hydraulic lines.
In accordance with FIG. 2, a relatively low pressure fluid from the high capacity fluid power supply 50 is introduced through check valve 40 into the pressure line 51 to increase the speed limit of the hydraulic cylinder 1 (FIG. 1), as the pressure rate in line 51 is sufficiently declined. Actually, the hydraulic power supply 50 is being entered into the operation just after the spool of valve 2 passes its critical point, beyond which the pressure P2 in line 51 is dropped below the minimum regulated pressure P2min.
The schematic shown on FIG. 1 is assymmetrical, relative to the chambers 10 and 11. the functional operation of this schematic can be still better visualized by considering its generalized model, which is presented on FIG. 3-A and is accompanied by the related pressure-compensated flow characteristic
F10 =Kl &#916;X
of valve 2. the fluid power means 3 shown on FIG. 3-A, combine the fluid power supply means 3-1 and the regulators 3-3, which are shown on FIG. 1.
The concept of preventing a substantial schematic operation interference.
The pressures P10 and P11 have to be high enough to prevent the full decompression of chambers 10 and 11 under the dynamic operation conditions. On the other hand, the pressure drop command signals ΔP2 and ΔP3 have to be small enough to improve the system energy efficiency.
The schematic shown on FIG. 4 is assymmetrical, relative to the chambers 10 and 11. The functional operation of this schematic can be still better visualized by considering its generalized model, which is presented on FIG. 5-A and is accompanied by the related flow characteristics
F11 =-Kl &#916;X
of valve 2. The first of these flow characteristics is pressure-compensated. The fluid power means 3 shown on FIG. 5-A, combine the fluid power supply means 3-1 and the regulator 3-3, which are shown on FIG. 4.
The schematic shown on FIG. 6 is related to the load adaptive hydraulic postion servomechanism having two controllable chambers and loadable in both directions. This schematic is provided with the five-way spool valve and is easily understood when compared with FIG. 4. The loadable chamber 10 is controlled as before except that the supply signal line SL2 is communicated (commutated) with chamber 10 through check valve 5. The second loadable chamber--chamber 11--is commutated by valve 2 with the supply power line L6 and with the exhaust power line L5. The line L6 is connected to line L2. The supply signal line SL2 is also communicated (commutated) with chamber 11 through check valve 6.
The exhaust line L5 is a separate counterpressure line which is provided with an additional exhaust line pressure drop feedback control system including an additional exhaust line pressure drop regulator 3-4 which is shown on FIG. 6. the related exhaust signal line SL5 transmitting signal P05, is connected to line 12 of chamber 11. The counterpressure maintained in line L5 by the additional exhaust line pressure drop feedback control system, is:
P5 =P05 -&#916;P5,
where ΔP5 is the related pressure drop command signal.
The check valve logic makes it possible for the line SL2 to select one of two chambers, whichever has the higher pressure rate, causing no problem for maintaining the supply fluid pressure drop across valve 2, as well as for the dynamic stability of the fluid motor position feedback control system. A very small throttle valve 19 connecting line SL2 with the tank line 52, is helpful is extracting signal P02.
The schematic shown on FIG. 6 is symmetrical, relative to the chambers 10 and 11. the functional operation of this schematic can be still better visualized by considering its generalized model, which is presented on FIG. 7-A and is accompanied by the related pressure-compensated flow characteristics
of valve 2. The fluid power means 3 shown on FIG. 7-A, combine the fluid power supply means 3-1, the regulators 3-3, 3-4, and the small throttle valve 19, which are shown on FIG. 6.
Position feedback control means.
It should be noted that transition from the conventional fluid position servomechanisms to the load adaptive fluid position servomechanisms does not change the part of the system which is outlined by block 4. The optional physical structure of the position feedback control means is disclosed in numerous prior art patents and publications describing the conventional fluid motor position feedback control systems and the related position feedback control technique--see, for example, the above named books and also:
a) Davis, S. A. and B. K. Ledgerwood, "Electromechanical Components for Servomechanisms". New York: McGraw-Hill, 1961.
c) Analog Devices, Inc., "Analog-Digital Conversion Handbook", Edited by Sheingold D. H., Third Edition. Englewood Cliffs, N.J.: Prentice-Hall, 1986.
d) D'Souza, A. F., "Design of control systems". Englewood Cliffs, N.J.: Prentice-Hall, 1988.
1. The motor position Xl is the position of moving part 21 (piston, shaft and so on) of the fluid motor 1. In fact, the motor position Xl can also be viewed as a mechanical signal--the output position signal of the fluid motor position feedback control system being considered.
2. The motor position Xl is measured by the position feedback control means due to the position sensor, which is included into block 4 and is connected to the moving part 21 of the fluid motor 1.
3. In the electrohydraulic position servomechanisms, and electromechanical position sensor can be analog or digital. The analog position sensor employs an analog transducer, such as a linear variable differential, a synchro transformer, a resolver and so on. The digital position sensor may include a digital transducer, such as an optical encorder. the digital position sensor can also be introduced by an analog-digital combination, such as the resolver and the resolver-to-digital converter--see, for example, chapter 14 of the above named book of Analog devices, Inc.
4. It is to say that in the electrohydraulic analog or digital, position servomechanisms, the motor position feedback signal CXl (or the like) is generated by the electromechanical sensor in a form of the electrical, analog or digital, signal, respectively.
6. In the hydromechanical postion servomechanisms, the mechanical postion sensor is simply a mechanical connection to the moving part 21 of the fluid motor 1. In this case, the motor position feedback signal CXl is a mechanical signal. The position input-command signal Xo is also a mechanical signal.
(a) the original position feedback control error signal ΔXor is produced as a difference between the position input-command signal Xo and the motor position feedback signal CXl ;
(b) the original position feedback control error signal ΔXor is finally translated into the manipulted postion feedback control error singal ΔX;
(c) it can be said that the manipulated position feedback control error signal ΔX is derived in accordance with a difference between the position input-command signal Xo and the output position signal Xl ;
(d) the manipulated feedback control error signal ΔX is a mechanical signal, which is identified with the spool displacement of valve 2 from the neutral spool position ΔX≅0.
8. In the electrohydraulic position servomechanisms, the spool of valve 2 is most often actuated through the hydraulic amplifier of the position feedback control means. the spool valve 2, the hydraulic amplifier, and the electrical torque motor are usually integrated into what is called an "electrohydraulic servovalve" .
9. In the hydromechanical postion servomechanisms, the spool of valve 2 is also most often actuated through the hydraulic amplifier of the position feedback control means. The spool valve 2 and the hydraulic amplifier are usually integrated into what is called a "servovalve".
10. Still more comprehensive descriptioon of the optional position feedback control means (block 4) can be found in the prior art patents and publications including the books already named above.
A concept of load adaptive regeneration of energy.
In applications, like high-speed shrot-stroke hydraulic presses, where a potential energy associated with the compressed hydraulic fluid is substantial in defining the system energy efficiency, a regeneration of this energy can be justified. FIG. 9 is originated by combining FIG. 1 and FIG. 2. However, the regulator 3-3 is replaced by a variable displacement motor 65 having a variable dsplacement means 67, a pressure line 77, and a tank line 73. The motor 65 is connected through line 77 to line L3 and has a "common shaft" 72 with the variable displacement pump 58. The variable displacement means 67 is modulated by the exhaust line pressure drop feedback signal, which is equal P03 -P3 and is measured between the exhaust power line L3 (through line 75) and the related signal line SL3. The exhaust line pressure drop feedback control system including motor 65, maintains the exhaust fluid pressure drop P03 -P3 across spool valve 2 by varying the counterpressure
P3 =P03 -&#916;P3 in the exhaust line L3 by the variable displacement means 67. A fly wheel 94 is attached to the shaft 72 and is driven by motor 65. The pump 58 is generally driven by a primary motor 100, by the motor 65 and by the fly wheel 94. As a result, the potential energy of the fluid compressed in chamber 10 and, hence, the exhaust fluid energy of the exhaust fluid flow passing through line L3, is converted into a kinetic energy of motor 65 and the related rotated mass including fly wheel 94. This kinetic energy is finally reused through the supply power line L2 by the supply line pressure drop feedback control system. FIG. 9 also shows the frame 190 (of hydraulic press 192), against which the chamber 10 of cylinder 1 is loaded.
It is understood that availability of the motor position input-command signal Xo, makes it possible not only to regulate the fluid motor position Xl, but also to control the fluid motor velocity. It is now assumed, for simplicity, that motor vehicle is moving only in a horizontal direction. Accordingly, it is also assumed that five-way spool valve 2 is working now as a one-directional valve--it's spool can be moved only down from the neutral spool position only (which is shown on FIGS. 10 and 11). Note that FIGS. 10 and 11 are used only for a further study of load adaptive regeneration of energy. The related velocity feedback control (FIG. 16) and especially the related open-loop control (FIGS. 17 to 22, and 26) are, of course, more likely to be used for the motor vehicle type applications.
In general, the load adaptive, position feedback controlled, variable speed drive systems may incorporate a built-in regenerating circuitry or an independent regenerating circuitry. The drive system incorporating the built-in regenerating circuitry is shown on FIG. 10 which is originated by combining FIG. 6 and FIG. 2. However, the fluid power supply of FIG. 2 is represented on FIG. 10 mainly by pump 58. The regulator 3-3 is not needed now and, therefore, is not shown on FIG. 10. On the other hand, the regulator 3-4 is replaced by a variable displacement motor 66 having a variable displacement means 68, tank line 74, and pressure line 78 which is connected to line L5. The hydraulic cylinder 1 shown on FIG. 6 is replaced by the rotational hydraulic motor 1 which is loaded by a load 96 representing a mass of the motor vehicle. the fly wheel 94 is attacjed to the common shaft 72 connecting pump 58, motor 66, and the primary motor 100 of the motor vehicle. The variable displacement means 68 is modulated by the exhaust line pressure drop feedback signal, which is equal P05 -P5 and is measured between line L5 (through line 76) and the related signal line SL5. The exhaust line pressure drop feedback control system including the variable displacement motor 66, regulates the exhaust fluid pressure drop P05 -P5 across spool valve 2 by varying the counterpressure
P5 =P05 -&#916;P5 in the exhaust power line L5 by the variable displacement means 68. In a simple case, the motor position command signal Xo being varied with the constant speed, will generate a relatively constant velocity of motor 1 and the positional lag ΔX proportional to this velocity. In general, the shaft velocity of motor 1 can be controlled by the speed of varying the motor position command signal Xo. During the deceleration of the motor vehicle, the kinetic energy accumulated by a mass of the motor vehicle (load 96) is transmitted through motor 66 to the fly wheel 94. During the following acceleration of the motor vehicle, the kinetic energy accumulated by fly wheel 94 is transmitted back through energy between the motor vehicle (load 96) and the flywheel 94 is correlated with the fly wheel speed fluctuations. It is assumed that a speed-torque characteristic of the primary motor 100 (such as the electrical motor or the internal-combustion engine) is soft enough to allow these fly wheel speed fluctuations.
The variable speed primary motor 92, the related speed control circuitry which is meant to be included into block 92, and the variable displacement primary pump 90 are all included into the primary supply line pressure drop feedback control system. The variable speed primary motor 92 is modulated by the primary supply line pressure drop feedback signal P2 -P02, which is measured between line 54 (line 91) and line SL2. As a result, the primary supply line pressure drop feedback control system is capable of maintaining the primary supply fluid pressure drop P2 -P02 across spool valve 2 by varying the primary pressure rate
P2 =P02 +&#916;P2 in the supply power line 54 by varying the speed of the variable speed primary motor 92, such as the internal-combustion engine or the electrical motor.
On the other hand, the pump 58, shown on FIG. 10 is replaced on FIG. 11 by an assisting variable displacement pump 55 having an assisting variable displacement means 57 to make up an assisting supply line pressure drop feedback control system. The line 36 of pump 55 is connected through check valve 44 to line L2. The assisting variable displacement means 57 is modulated by an assisting supply line pressure drop feedback signal P2R -P02, which is measured between line 30 (through line 32) and line SL2. As a result, the assisting supply line pressure drop feedback control system is capable of maintaining the assisting supply fluid pressure drop P2R -P02 across spool valve 2 by varying the assisting pressure rate
P2R =P02 +&#916;P2R in the supply power line 30. During the operation, the supply power line L2 is switched over to line 54 or line 30, whichever has the higher pressure rate, by the logic of check valves 40 and 44. The assisting pressure drop command signal ΔP2R is selected to be just slightly larger than the pressure drop command signal ΔP2. Accordingly, while the speed of fly wheel 94 is still relatively high, the assisting pressure
P2R =P02 +&#916;P2R will exceed the primary pressure
P2 =P02 +&#916;P2 and, hence, the supply power line L2 will be connected to line 30 through check valve 44. At any other time, the supply power line L2 is connected to line 54 through check valve 40. In other words, the independent regenerating circuitry, including motor 66, pump 55, and fly wheel 94, is given a priority in supplying the fluid energy to the supply power line L2. this independent regenerating circuitry is automatically entering into and is automatically withdrawing from the regulation of assisting the supply fluid pressure drip across spool valve 2. The exchange of kinetic energy between the motor vehicle (load 96) and the fly wheel 94 is basically accomplished as considered above (for the schematic shown on FIG. 10); however, the undesirable interference between the primary motor 92, such as the electrical motor or the internal-combustion engine, and the regenerating circuitry is now eliminated. It should be noted that the variable delivery means 93 of pump 90 can be employed for achieving some energy efficiency of the internal-combustion engine 92. In fact, these additional control objectives can be similar to those which are usually persuaded in regulating the standart automotive transmissions of motor vehicles.
It should also be noted that schematic shown on FIG. 11 is of a very general nature and can be further modified and (or) simplified. If there is no additional control objectives, such as just indicated, the variable speed primary motor 92 is replaced by a relatively constant speed primary motor 100, while the variable delivery means 93 of the primary pump 90 is employed for maintaining the primary pressure
P2 =P02 +&#916;P2 in line 54. This case is illustrated by FIG. 12 which is a modification of FIG. 11 for the hydraulic press type application. In this case, the rotational hydraulic motor 1 is replaced by the double-acting cylinder 1. The exhaust line pressure drop feedback control system including motor 66 is adapted to maintain pressure
P3 =P03 -&#916;P3 in the exhaust power line L3. The potential energy of the hydraulic fluid compressed in chamber 10 of cylinder 1 is regenerated now by the independent regeneraing circuitry through the exhaust power line L3 and the related exhaust line pressure drop feedback control system including motor 66. In fact, the schematic of FIG. 12 is easily understood just by comparison with FIG. 11 and FIG. 9. For simplicity, the additional fluid power supply 50 is not shown on FIG. 12.
Some preliminary generalization.
It is noted that word "LOAD" within block 96 (see FIGS. 10, 11, 16 to 22, and 26) is also considered to be a substitute for the words "the motor load means" and is related to all the possible applications of this invention. In a case of motor vehicle applications, the motor load means include a mass of a "wheeled" motor vwehicle (as it is specifically indicated on the schematic of FIG. 22).
b) the load adaptive fluid motor control systems having an energy regenerating circuitry for regenerating the load related energy (see FIGS. 9 to 12). This second type of load adaptive fluid motor control sytems can also be referred to as the regenerative adaptive fluid motor control systems. Still other modifications of the regenerative adaptive fluid motor control systems will be considered later.
General criterion of dynamic stability of combined component systems.
The load adaptive fluid motor position feedback control system is typically a combination of at least three component feedback control systems--the fluid motor position feedback control system, at least one exhaust line pressure drop feedback control system, and at least one supply line pressure drop feedback control system. In order to prevent a possible complex interference between the combined components systems, the pressure drop feedback control systems must be properly regulated both with respect to the fluid motor position feedback control system and with respect to each other. Accordingly, a general criterion of dynamic stability of combined component systems (which are stable while separated) can be introduced by a set of provisions (or by a combination of concepts) as follows:
(1) preventing a substantial schematic operation interfeernce between the pressure drop feedback control systems and the fluid motor osition feedback control system (this concept has been already discussed before);
(2) providing a significant dynamic performance superiority for the pressure drop feedback control systems against the fluid motor position feedback control system, in order to prevent a substantial dynamic operation interference between the pressure drop feedback control systems and teh fluid motor position feedback control system (this concept will be discussed later):
The concept of preventing a substantial pressure drop regulation interference.
(a) a motor static speed characteristic describing the hydraulic motor speed versus the valve spool displacement, under the assumption that the hydraulic fluid is not compressible;
(b) a compression-decompression speed versus the valve spool displacement, under the assumption that the hydraulic motor speed is equal to zero. As a result, the speed control of fluid motor 1 by any pressure drop feedback control system is generally effected by the processes of compression-decompression of hydraulic fluid and, therefore, is substantially inaccurate. This speed control is, of course, still further effected by some other factors, such as the static and dynamic errows in maintaining the pressure drop.
The destructive conditions of pressure drop regulation interference can be avoided simply by preventing a simultaneous speed control of fluid motor 1 by two pressure drop feedback control systems, that is by the supply and exhaust line pressure drop feedback control systems. Without the loss of generality, the concept of preventing a pressure drop regulation interference is considered further more specifically for two examplified groops of schematics as follows:
(b) the load adaptive schematics ahving two loadable chambers, and therefore, having two pressure drop feedback control systems which potentially may participate simultaneously in controlling the speed of motor 1--see FIGS. 11 and 16 to 22.
In the first groop of load adaptive schematics, the supply and exhaust line pressure drop feedback control systems will obviously never interfere. In these schematics, the speed of motor 1 is usually controlled only by a supply line pressure drop feedback control system (that is by the primary supply line pressure drop feedback control system or by the assisting supply line pressure drop feedback control system). the motor-cylinder 1 having only one loadable chamber is assumed to be loaded in only one direction by a static force. Accordingly, the motor load is measured by the pressure signals P02 =P03. The exhaust line pressure drop feedback control system is ussally in operation only during the decompression of chamber 10 of motor 1.
&#916;P5 &gt;&#916;P2R &gt;&#916;P2            (3)
Let's consider now more specifically the second groop of load adaptive schematics. the magnitude and direction of the motor load is conveniently measured by the pressure signals P02 and P05, which are implemented for controlling the supply and exhaust line pressure drop feedback systems, erspectively. the load pressure signals P02 and P05 are also used for controlling the sequence of operation of these pressure drop feedback control sytems, as it is illustrated below.
1. the wheeled vehicle is moving with a constant speed. In this case, the motor load is positive, the load pressure signal P02 is relatively large, and the primary supply line pressure drop feedback control system is activated to maintain the primary supply fluid pressure drop
P2 -P02 =&#916;P2 across spool valve 2. On the other hand, the pressure signal P05 is very small, and therefore, the exhaust line pressure drop feedback control system is not activated to maintain the exhaust fluid pressure drop
P05 -P5 =&#916;P5 across spool valve 2. Note that in this case, the exhaust fluid pressure drop P05 -P5 is equal approximately to the primary supply line pressure drop command signal ΔP2, provided that supply and exhaust openings of valve 2 are identical. Note also that if P5 ≅0:
P05 &#8773;&#916;P2 &lt;&#916;P5.
2. The wheeled vehicle is decelerated. In this case, the motor load is megative, the load pressure signal P05 is large, and the exhaust line pressure drop feedback control system is activated to maintain the exhaust fluid pressure drop
P05 -P5 =&#916;P5 across spool valve 2. On the other hand, the pressure P02 is very small and has a tendency of dropping "below zero". In practical applications, a vacuum in motor line L1 must be prevented by introducing a check valve (such as check valve 155 on FIGS. 20 and 22) connecting line L1 with the oil tank 62 (or with a low-pressure hydraulic accumulator). Note that by virtue of expression (3), the process of deceleration should be started onle after this check valve is open. It is understood that in this setuation, the supply line pressure drop feedback control sytems have no effect on the process of deceleration of motor 1.
4. The wheeled vehicle is accelerated. In this case, the motor load is positive, the load pressure signal P02 is large, and teh assisting supply line pressure drop feedback control sytem is activated to maintain the assisting supply fluid pressure drop
P2R -P02 =&#916;P2R across spool valve 2. On the other hand, the pressure signal P05 is very small, and therefore, the exhaust line pressure drop feedback control system is not activated to maintain the exhaust fluid pressure drop
P05 -P5 =&#916;P2R across spool valve 2. Note that in this case, the exhaust fluid pressure drop P05 -P5 is equal approximately to the assisting supply line pressure drop command signal ΔP2R, provided that supply and exhaust openings of valve 2 are identical. Note also that if P5 ≅0:
P05 &#8773;&#916;P2R &lt;&#916;P5.
Finally, it can be concluded that in the load adaptive fluid motor control systems, the functions of the motor laod are not limited to controlling separatelyv each of the pressure drop feedback control systems. Indeed, the functions of the motor load are generally extended to include also the control over the sequence of operation of the supply and exhaust line pressure drop feedback control sytems, in order to prevent a possible pressure drop regulation interference between these pressure drop feedback control systems.
The concept of providing a significant dynamic performance superiority.
It is important to stress that the concept of providing a significant dynamic performance superiority for the pressure drop feedback control systems against the fluid motor position feedback control system is an integral part of this invention. This concept introduces a criterion of dynamic stability of combined component systems which are stable klwhile separated (provided that the concept of preventing a schematic operation interference and the concept of preventing a pressure drop regulation interference are already properly implemented). As it is already mentioned above, the load adaptive fluid motor position feedback control system is typically a combination of at least three component feedback control systems--the fluid motor position feedback control system, at least one exhaust line pressure drop feedback control system, and at least one supply line pressure drop feedback control system.
a) Shinners S. M., "Modern Control System Theory and Application", Second Edition. Reading, Massachusetts: Addison-Wesley Publishing Company, 1972.
b) Davis S. A., "Feedback and Control System". New York: Simon and Shuster, 1974.
It is further assumed that each of the separate component systems is linearized and, thereby, is basically described by the ordinary linear differential equations with constant coefficients, as it is usually done in the engineering calculations of electrodydraulic, hydromechanical, and hydraulic closed-loop systems. Note that the fluid motor position feedback control system (separated from other component systems) is especially easy to linearized if to admit that the expected regulation of the exhaust and supply fluid pressure drops is already "in place".
Let's consider (without the loss of generality) the load adaptive fluid motor position feedback control system incorporating only three component systems--the fluid motor position feedback control system, only one exhaust line pressure drop feedback control system. In this case, the criterion of dynamic stability of combined component systems can be reduced to only five conditions as follows:
(4) preventing a substantial dynamic operation interference between teh exhaust fluid pressure drop regulation and the motor position regulation by providing a significant dynamic performance superiority for the exhaust line pressure drop feedback control system against the fluid motor position feedback control system;
(5) preventing a substantial dynamic operation interference between the supply sluid pressure drop regulation and the motor postion regulation by providing a significant dynamic performance superiority for the supply line pressure drop feedback control system against the fluid motor position feedback control sytem.
The presented above--first, second, and third conditions of dynamic stability are the requirements to the separate component systems. The fourth and fifth conditions of dynamic stability define limitations which must be imposed on the separate component systems in order to combine them together. The design of the separate closed-loop systems for the dynamic stability and required performance is well known in the art, as already emphasixed above. For this reason, it is further assumed, for simplicity, that the first three conditions of dynamic stability are always satisfied if the last two conditions of dynamic stability are satisfied.
The provision of preventing "a substantial dynamic operation interference" is associated with the concept of providing "a significant dynamic performance superiority". The term "a substantial dynamic operation interference" is introduced to characterize the dynamic instability of combined component systems which are stable while separated. This dynamic instability can be detected in a frequency domain or in a time domain by ##EQU3## respectively, where:
ωRp and tfp are the resonant frequency and the final transient time (respectively) of the fluid motor position feedback control system;
The closed-loop resonant frequency ωR (that is ωRp or ωRd) is located by a resonant peak of the closed-loop frequency-response characteristic and, therefore, is also often called "a peaking frequency". This resonant peak is typically observed on a plot of the amplitude portion of the closed-loop frequency-response characteristic. However, the resonant peak is observed only if the system is underdamped. For this reason and for simplicity, the appropriate approximations of the ratio ##EQU4## can also be employed. For example, the possible approximation is: ##EQU5## where: ωbp and ωbd are the closed-loop bandwidths for the position feedback control system and the pressure drop feedback control system, respectively.
Moreover, as the first approach (roughly approximately): ##EQU6## where: ωocp and ωocd are the open-loop cross-over frequencies for the position feedback control system and the pressure drop feedback control system, respectively.
The final transient time tf (that is tfp or tfp) of the closed-loop system is the total output-response time to the step input. the transient time tf i also often called "a settling time" and is measured between t=0 and t=tf --when the response is almost completed. The method of defining the closed-loop resonant frequency ωR, the closed-loop bandwidth ωb, the open-loop cross-over frequency ωoc, and the closed-loop final transient time tf are well known in the art--see, for example, the above named books of S. M. Shinners, S. A. Davis, and A. F. D'Souza.
Now, it is understood that if "a substantial dynamic operation interference" is identified by (4) or (5), then "a significant dynamic performance superiority" should be identified by: ##EQU7## where: S.sub.ω is the minimum stability margin in a frequency domain,
These minimum allowable stability margins can be specified approximately as: S.sub.ω ≅10 and St ≅10.
The formulas (8) and (9) must be introduced into the design of the load adaptive fluid motor position feedback control system. The way to do this is to design the separate component systems for the dynamic stability and required performance while the inequalities (8) and (9) for the combined component systems are satisfied. The approximate connections between the resonant frequencies and some other typical frequencies ahve been already illustrated by equations (6) and (7).
While the equations (8) and (9) are valid for the second- and higher-order differential equations, the principal relationship between the final transient time tf and the resonant frequency ωR is more easy to illustrate for the second-order equation ##EQU8## which can be modified as: ##EQU9## where: y and z are the input and output, respectively;
the undamped natural frequency ω2 =√B2 ;
the damping coefficient ##EQU10## the dimensionless time τ=ω2 t. For this second order equation, the output responses Z(τ) to a unit step input (while the initial conditions are zero) for various values of ξ are well known in the art--see, for example, the above named books of S. M. Shinners and S. A. Davis.
Note that for the second-order equation ##EQU11## and, hence the final transient time ##EQU12## The final transient dimensionless time τf is a function of the damping coefficient ξ . More generally, when the right part of the second-order equation is more complicated, the final transient dimensionless time τf is also effected by the right part of this equation.
In the case of using second-order systems, the ratio ##EQU13## can be approximated by the ratio ##EQU14## and therefore: ##EQU15## where: ω2p and τfp are the undamped natural frequency and the final transient dimensionless time, respectively, for the position feedback control system;
ω2d and τfd are the undamped natural frequency and and the final transient dimensionless time, respectively, for the pressure drop feedback control system.
In general, for the second- and higher-order systems, it can be still stated, by the analogy with the second-order system, that the ratio ##EQU16## is basically dependent on the ratio ##EQU17## and is further dependent on the secondary factors, such as the effects of damping. It is to say that expression (8) can be viewed as a basic (or main) test on the dynamic stability of combined components systems which are stable while separated. This main test is needed to prevent the frequency resonance type phenomenon between the component systems. However, an additional test--equation (9) is still needed to prevent the operational break-down of the combined component systems.
a) the expression (8) alone is a necessary criterion for the dynamic stability of combined component systems which are stable while separated;
b) the expressions (8) and (9) together are a sufficient criterion for the dynamic stability of combined component systems which are stable while separated.
Of course, still other terms, interpretations, and measurements can be generally found to further characterize what have been just clearly defined--based ont he physical considerations--as being "a substantial dynamic operation interference" and "a significant dynamic performance superiority".
Adaptive fluid position feedback control: the scope of expected applications.
the load adaptive fluid position servomechanisms make it possible to substantially improve the energy, performance, and environmental characteristics of the position feedback control in comparison with the conventional fluid position servomechanisms. In particular, the load adaptive fluid position servomechanisms may combine the high energy-efficient and quiet operation with the relatively high speed and accuracy of performance. The artificial load adaptability of load adaptive fluid position servomechanisms is achieved by regulating the exhaust and supply fluid pressure drops by the eklxhaust and supply line pressure drop feedback control systems, respectively.
Because the artificial load adaptability is implemented by relatively simple design means, the load adaptive fluid postion servomechanisms combine the very best qualities of the conventional fluid motor position feedback control systems and the naturally load adaptive, electric motor position feedback control systems. Moreover, the load adaptive fluid position servomechanisms may incorporate the energy regenerating circuitry.
Accordingly, the scope of potential applications of the adaptive hydraulic position servomechanisms being considered is extremely wide. So, it is expected that the conventional hydraulic (electrohydraulic or hydromechanical) position servomechanisms will be replaced almost everywhere by the load adaptive hydraulic position servomechanisms. It is also expected that many naturally load adaptive, electric motor position feedback control sytems will also be replaced by the artificially load adaptive, hydraulic motor position feedback control systems.
For example, the schematics shown on FIGS. 9 and 12 can be used for constructing the high energy-efficint hydraulic presses. the load adaptive hydraulic press may have advantages against the conventional hydraulic and mechanical presses due to a combination of factors as follows:
Finally, it should be noted that schematics shown on FIGS. 4 and 12, make it possible to absorb the shocks generated by a sudden disappearance of load, for example, during the punching operations on hydraulic presses. This is accomplished by decelerating the motor-cylinder 1 just before the load disappears to provide the valve spool to be close to its neutral point (Δx=0). Just after the load disappears, the position feedback control system locks the fluid in chamber 11 or even connects this fluid with the supply power line L2. It means that the potential energy of the fluid compressed in chamber 10, is used mostly to compress the fluid in chamber 11 and, finally, is converted to a heat.
Adaptive fluid motor feedback control.
FIG. 13 shows a generalized model of the load adatpvie fluid motor output feedback control systems which include an independent energy regenerating circuitry. This model can be viewed as a further development of FIG. 8 in view of Figs. 11 and 12 and is mostly self-explanatory. Note that the position feedback control means (block 4) and the related signals Xl, Xo, and ΔX, which are shown on FIG. 8, are replaced by the (motor) output feedback control means (block 4-M) and the related signals Ml, Mo, ΔM, which are shown on FIG. 13. More specifically, the motor position Xl, the position input-command signal Xo, and the position feedback control error signal ΔX are replaced by their "generic equivalents"--the motor output Ml, the related input-command signal Mo, and the motor output feedback control erro signal ΔM, respectively. by the analogy with the load adaptive fluid motor position feedback control system, the motor output control error signal ΔM is produced by the output feedback control means (block 4-M) in accordance with a difference between the input-command signal Mo and the motor output Ml.
A generalized model of the regenerative adaptive fluid velocity servomechanisms is shown on FIG. 14. This model is derived from the one shown on FIG. 13 just by replacing the (motor) output feedback control means (block 4-M) and the related signals Ml, Mo, and ΔM by the velocity feedback control means (block 4-V) and the related signals Vl, Vo, and ΔV, respectively. It is to say that the schematics for the adaptive fluid velocity servomechanisms being considered can also be derived from the above presented schematics for the adaptive fluid position servomechanisms just by replacing the position feedback control means (block 4) and the related signals Xl, Xo, and ΔX by the velocity feedback control means (block 4-V) and the related signal Vl, Vo, and ΔV, respectively. The motor velocity Vl is the velocity of the moving part 21 of the fluid motor 1. In fact, the motor velocity Vl can also be viewed as a mechanical signal--the output velocity signal of the load adaptive fluid motor velocity feedback control system. The motor velocity Vl is measured by the velocity sensor, which is included into block 4-V and is connected to the moving part 21 of the fluid motor 1. The velocity feedback control error signal ΔV is produced by the velocity feedback control means (block 4-V) in accordance with a difference between the velocity input-command signal Vo and the motor velocity Vl. It is reminded that at the balance of the position feedback control: ΔX≅0 and the spool of valve 2 is in the neutral spool position for any given value of the position command signal Xo. Accordingly, at the balance of the velocity feedback control ΔV≅0; however, the spool of valve 2 is not generally in the neutral spool position but is in the position which corresponds to the given value of the velocity command signal Vo. It is already understood that the velocity feedback control means (block 4-V) can be still further described basically by the analogy with the above brief description of the position feedback control means (block 4). The optional physical structure of the velocity feedback control means (block 4-V) is also disclosed by numerous prior art patents and publications describing the conventional fluid motor velocity feedback control systems and the related velocity feedback control technique--see, for example the books already named above.
The schematic shown on FIG. 16 can be used for constructing the load adaptive, velocity feedback controlled, fluid power drive systems for the motor vehicles. This schematic is derived from the one shown on FIG. 11 by replacing the position feedback control means (block 4) and the related signals Xo, X1, and ΔX by the velocity feedback control means (block 4-V) and the related signals Vo, V1, and ΔV, respectively. In addition and for simplicity, the five-way spool valve 2 shown on FIG. 11 is replaced by the four-way spool valve 2 shown on FIG. 16. Accordingly, the supply power line L6 and the exhaust power line L3 are eliminated. The four-way spool valve 2 is considered now to be a one-directional valve--it's spool can be moved only down from the neutral spool position and can be returned back to the neutral spool position only (which is shown on FIG. 16).
A generalized model of the regenerative adaptive fluid motor open-loop control systems is presented by FIG. 15 which is derived from FIG. 13 just by eliminating the output feedback control means (block 4-M) and the related signals Mo, M1, and ΔM. The schematics for the load adaptive fluid motor open-loop control systems can be derived from the above presented schematics for the load adaptive fluid motor position feedback control systems just by eliminating the position feedback control means (block 4) and the related signal Xo, X1, and ΔX.
The open-loop schematic, which is shown on FIG. 17, is derived from the one shown on FIG. 16 just by eliminating the velocity feedback control means (block 4-V) and the related signals Vo, V1, and ΔV. The schematic of FIG. 17 can be used for constructing the high energy-efficient load adaptive motor vehicles, as it will be still further discussed later.
General Principle of Coordinated Control: The Constructive Effect of Motor Load
As it is already mentioned above, a regenerative adaptive fluid motor control system is typically a combination of at least three component control systems--a fluid motor control system, at least one exhaust line pressure drop feedback control system, and at least one supply line pressure drop feedback control system. The fluid motor control system may or may not include the output feedback control means.
In order to illustrate this principle more specifically, let's consider, for example, a regenerative adaptive fluid motor drive system for the motor vehicle. In accordance with FIGS. 10, 11, 16, and 17, the magnitude and direction of motor load of motor 1 are conveniently measured by the pressure signals P02 and P05. These pressure signals can also be viewed as the load related, input-command signals for the supply and exhaust line pressure drop feedback control systems, respectively. It means that all the pressure drop feedback control systems are, indeed, controlled in unison by the motor load of motor 1.
SOME EXAMPLIFIED SYSTEMS
Adaptive Fluid Control and the Motor Vehicles
The load adaptive motor vehicle drive systems, like the one shown on FIG. 17, may have advantages against the conventional motor vehicle drive systems in terms of such critical characteristics as energy efficiency, environmental efficiency, reliability, controlability, and dynamic performance. Some of the underlying considerations are:
3. The exhaust fluid pressure drop regulation and the independent regenerating circuitry makes it possible to create the schematic conditions, under which the energy accumulated during the deceleration of the motor vehicle is reused during the following acceleration of the motor vehicle. The energy accumulated during the vehicle down-hill motion will also be reused.
Adaptive Fluid Control and the City Transit Buses
The load adaptive drive system, such as shown on FIG. 17, is especially effective in application to the buses which operate within the cities, where a stop-and-go traffic creates the untolerable waste of energy, as well as the untolerable level of air pollution. Let's assume, for simplicity, that the bus is moving in a horizontal direction only. And let's consider, for example, the process of bus deceleration--acceleration beginning from the moment when the bus is moving with some average constant speed and the "red light" is ahead. Up to this moment the spool of valve 2 have been hold pushed partially down by the driver, so that this valve is partially open.
In the process of bus deceleration:
the spool of valve 2 is being moved up- to close this valve;
the energy accumulated by fly wheel 94 is transmitted through pump 55, check valve 44, lines L2 and L1 to the motor 1. When the energy accumulator 94 is almost discharged, the pressure P2R is being dropped so that the check valve 44 is closed, and the check valve 40 is open permitting the engine 92 to supply the power flow to the fluid motor 1.
Adaptive Fluid Control with the Hydraulic Accumulator
The regenerative adaptive fluid control schematic which is shown on FIG. 18, can also be used for the motor vehicle applications, and in particular, for the buses which operate within the cities. This schematic will be studied by comparison with the one shown on FIG. 17. The fly wheel 94 shown on FIG. 17 is substituted by a hydraulic accumulator 122 shown on FIG. 18. Accordingly, the exhaust line variable displacement motor 66 is replaced by the exhaust line constant displacement motor 116 driving the exhaust line variable displacement pump 120 which is powering the hydraulic accumulator 122 through check valve 136. The exhaust line variable displacement pump 120 is provided with the variable displacement means 130 which is used to maintain counterpressure P5 =P05 -ΔP5 in the exhaust power line L5--as before. In other words, a counterpressure transformer including fluid motor 116, shaft 110, fluid pump 120, tank lines 74 and 134, and power lines 78 and 132, is implemented to make up the counterpressure varying and energy recupturing means of the exhaust line pressure drop feedback control system maintaining counterpressure P5 =P05 -ΔP5 in the exhaust power line L5.
Adaptive Fluid Control: The Combined Energy Accumulating Means
It is understood that many other modification and variations of regenerative adaptive fluid control schematics are possible. These schematics may include the fly wheel, the hydraulic accumulator, the electrical accumulator, or any combined energy accumulating means. The exemplified schematic showing the combined energy accumulating (and storing) means is presented by FIG. 19 which is basically a repetition of FIG. 18; however, two major components are added: the electrohydraulic energy converting means 142 and the electrical accumulator 144. In addition, and just for diversity of the drawings presented, the variable speed primary motor 92 is replaced by the constant speed primary motor 100, so that now the variable displacement mechanism 93 of pump 90 is used for regulating the supply fluid pressure drop P2 -P02 =ΔP2, as it was already illustrated by FIG. 12. As the hydraulic accumulator 122 is almost fully charged, an excess fluid is released from this accumulator, and a hydraulic energy of the excess fluid is converted through the electro-hydraulic energy converting means 142 to the electrical energy of electrical accumulator 144. On the other hand, as the hydraulic accumulator is almost fully discharged, the energy is transmitted back from the electrical accumulator 144 to the hydraulic accumulator 122.
Adaptive Fluid Control with a Variable Displacement Motor Driving the Load
FIG. 20 is basically a repetition of FIG. 18; however, the variable speed primary motor 92 is introduced now by the variable speed primary internal-combussion engine 92. In addition, the constant displacement motor 1 driving the load 96 is replaced by a variable displacement motor 150 driving the same load. The variable displacement means 152 of motor 150 are constructed to make-up the displacement feedback control system including a variable displacement mechanism (of motor 150) and employing a displacement feedback control errow signal ΔD, this errow signal is generated in accordance with a difference between a spool displacement (command signal) Do of valve 2 and a mechanism displacement (feedback signal) D1 of the variable displacement mechanism of motor 150. The displacement feedback control errow signal ΔD=Do -D1 is implemented for modulating the variable displacement mechanism of motor 150 for regulating the mechanism displacement D1 of the variable displacement mechanism of motor 150 in accordance with the spool displacement Do of valve 2. It should be emphasized that the displacement feedback control system, which is well known in the art, is, in fact, the position feedback control system and that, therefore, the general position feedback control technique, which is characterised above with respect to the fluid motor position feedback control system, is also basically applicable to the displacement feedback control system.
As the spool of valve 2 is moving down from the "zero" position shown on FIG. 20, there are two consecutive stages of speed regulation of motor 150: the lower speed range is produced by changing the actual (orifice) opening of valve 2, the higher speed range is produced by changing the displacement of motor 150. Speaking more specifically, the lower speed range of motor 150 is defined between the "zero" spool position and the point of full actual (orifice) opening of valve 2. Up to this point, the command signal Do is kept constant, so that the displacement of motor 150 is maximum and is not changed.
The higher speed range of motor 150 is located beyond the point of full actual (orifice) opening of valve 2. Beyond this point (due to the spool shape of valve 2) the further spool displacements do not change any more the opening of valve 2. On the other hand, beyond this point, the command signal Do is being reduced by the further spool displacements of valve 2. Accordingly, the displacement D1 =Do -ΔD of the variable displacement mechanism of motor 150 is being also reduced by the displacement feedback control system. The smaller the displacement of motor 150, the higher the speed of this motor (and the smaller the available torgue of this motor).
FIG. 20 also illustrates the use of check valves for restricting the maximum and minimum pressures in the hydraulic power lines. The check valve 154 is added to very efficiently restrict the maximum pressure in the exhaust motor line L4 by relieving an excess fluid from this line (through check valve 154) into the high-pressure hydraulic accumulator 122. The check valve 155 is added to effectively restrict the minimum pressure in the supply motor line L1 by connecting this line (through check valve 155) with the tank 62. Note that tank 62 can generally be replaced by a low-pressure hydraulic accumulator (accompanied by a small-supplemetary tank).
Adaptive Fluid Control with a Regenerative Braking Pump
In the motor vehicles, such as the City Transit Buses, the available braking torque should be usually substantially larger than the available accelerating torque. FIG. 21 is basically a repetition of FIG. 18; however, the constant displacement motor 1 driving the load 96 is also driving a regenerative braking variable displacement pump 170 which is used to increase the available regenerative braking torque. The tank line 176 of pump 170 is connected to tank 62. The pressure line 178 of pump 170 is connected through check valve 174 to the hydraulic accumulator 122. The flow output of pump 170 is regulated in accordance with the pressure rate P05 in the motor line L4 conducting a motor fluid flow from the fluid motor 1, as it is more specifically explained below.
The variable displacement means 99 of pump 170 are constructed to make-up a displacement feedback control system including a variable displacement mechanism (of pump 170) and employing a displacement feedback control error signal Δd. This errow signal is generated in accordance with a difference between a command-displacement signal do =Cp �P05 (where Cp is a constant coefficient) and a mechanism displacement (feedback signal) d1 of the variable displacement mechanism of pump 170. A pressure-displacement transducer converting the pressure signal P05 to the proportional command-displacement signal do =Cp �P05 is included into the variable displacement means 99 of pump 170. This transducer may incorporate, for example, a small spring-loaded hydraulic cylinder actuated by the pressure signal P05. The displacement feedback control errow signal Δd=do -d1 is implemented for modulating the variable displacement mechanism of pump 170 for regulating the mechanism displacement d1 of the variable displacement mechanism of pump 170 in accordance with the command signal do (and hence, in accordance with the pressure rate P05 =do /Cp in the motor line L4). It should be emphasized that the displacement feedback control system, which is well known in the art, is, in fact, the position feedback control system and that, therefore, the general position feedback control technique, which is characterised above with respect to the fluid motor position feedback control system, is also basically applicable to the displacement feedback control system.
In general, the displacement feedback control circuitry of pump 170 is adjusted so that, while the pressure P05 in the motor line L4 is comparatively low, this circuitry is not operative and d1 ≅0. As the pressure P05 in the motor line L4 is further raising-up, the displacement d1 of pump 170 is increasing accordingly, so that the total regenerative braking torque is properly distributed between the fluid motor 1 and the regenerative braking pump 170.
Adaptive Fluid Control Patterns
FIG. 22 is basically a repetition of FIG. 20; however, the variable speed primary internal-combussion engine 92 is now replaced by a relatively constant speed primary internal-combussion engine 100, while the variable displacement pump 90 is adapted now for maintaining the pressure P2 =P02 +ΔP2 in line 54, as it was already illustrated, for example, by FIG. 19. In addition, the variable displacement motor 118 and the constant displacement pump 114 are replaced by the constant displacement motor 198 and the variable displacement pump 194, in order to provide a wider range of regulation of pressure. P2R =P02 +ΔP2R in line 30. The assisting constant displacement motor 198 is powered by the hydraulic accumulator 122 (through shut-off valve 299) and is driving the assisting variable displacement pump 194 which is pumping the oil from tank 62 back into the accumulator 122 (through check valve 204 and shut-off valve 299). Actually, the output flow rate of accumulator 122 (in line 210) is equal to a difference between the input flow rate of motor 198 (in line 200) and the output flow rate of pump 194 (in line 124). The exhaust from motor 198 is used to power the line 30. The assisting variable displacement means 196 of pump 194 is modulated by the assisting pressure drop feedback signal P2R -P02 to maintain pressure P2R =P02 +ΔP2R in line 30--as before. The torque of pump 194 counterbalances the torque of motor 198. As the displacement of pump 194 is varied (by the assisting supply line pressure drop feedback control system) from the "maximum" to "zero", the pressure P2R in line 30 can be regulated from "almost zero" to the "maximum", accordingly. The check valve 208 connects line 132 (of pump 120) with the tank 62. The shut-off valve 299 is controlled by the load pressure signal P02. The check valve 208 and shut-off valve 299 are considered to be optional and are introduced only to illustrate more specifically some examplified patterns of controlling the load adaptive exchange of energy between the fluid motor and load means and the energy accumulating means. The related explanations are presented below.
In a general case, the motor vehicle is moving in a horizontal direction, up-hill, and down-hill, and with the different speeds, accelerations, and decelerations; however, all what counts for controlling the energy recupturing pressure drop feedback control system, is the load rate and direction (which are measured by the pressure signals P05 and P02). While the pressure signal P05 is very small, the pump 120 is actually disconnected from the accumulator 122, and the exhaust fluid flow is passing freely through motor 116 to the tank 62. As the pressure signal P05 is increasing, the kinetic energy of a vehicle mass is converted to the accumulated energy of accumulator 122.
Adaptive Fluid Control: Two Major Modifications
There are two major modifications of adaptive fluid control having an independent regenerating circuitry. The first major modification is identified by using the variable speed primary motor 92 for regulating the primary supply fluid pressure drop, as illustrated by FIGS. 11, 16, 17, 18, 20, and 21. The second major modification is identified by using the variable displacement mechanism of the variable displacement primary pump 90 for regulating the primary supply fluid pressure drop, as illustrated by FIGS. 12, 19, and 22. It is important to stress that these two major modifications are often convertible. For example, the schematics shown on FIGS. 11, 16, 17, 18, 20, and 21 can be modified by replacing the variable speed primary motor 92 by a constant speed primary motor 100 and by using the variable displacement mechanism of pump 90 for regulating the primary supply fluid pressure drop P2 -P02 =P2, as it is illustrated by FIGS. 12, 19, and 22. The transition to the modified schematics is further simplified by providing a constant speed control system for the variable speed motor 92 and by converting, thereby, this variable speed motor to a constant speed motor.
Regenerative Adaptive Drive Systems
It should be emphasized that the combined schematics providing an automatic transition from the one mode of operation to the other are especially attractive for the motor vehicle applications. The examplified modifications of combined schematics can be briefly characterized as follows.
2. The motor vehicle is first accelerated by actuating the variable displacement mechanism of pump 90--as illustrated by FIG. 22, is further accelerated by actuating the variable speed primary internal-combussion engine--as illustrated by FIG. 20, and is still further accelerated by actuating the variable displacement mechanism of motor 150--as illustrated by FIGS. 20 and 22. Note that in this case, the engine will be usually fully loaded only during the third stage of speed regulation--just after the displacement of motor 150 is sufficiently reduced. Note also that the minimum possible displacement of motor 150 must be restricted by the desirable maximum of engine load (which can be measured, for example, by the desirable maximum of pressure P02 in line L1 of motor 150).
4. The motor vehicle is provided with two relatively small engines. The first engine is usually in operation all the time. The second engine is usually switched-in only temporarily, while the motor vehicle is moving up-hill with a high speed. Each engine is driving a separate pump (line pump 90). Each engine-pump instalation is working with a separate spool valve (line spool valve 2).
10. Note that regenerative adaptive drive system, such as shown on FIG. 22, can be modified by replacing the "stationary" exhaust line energy recupturing means (the constant displacement motor 116 driving the variable displacement pump 120) and the "stationary" assisting variable delivery fluid power supply (the constant displacement motor 198 driving the variable displacement pump 194) by only one "shutle-type" motor-pump instalation including a constant displacement motor driving a variable displacement pump. Let's assume, for example, that wheeled vehicle is moving in a horizontal direction only. While the vehicle is decelerated, this motor-pump instalation is switched-in to perform as the "made-up" exhaust line energy recupturing means. While the vehicle is accelerated, this motor-pump instalation is switched-in to perform as the "made-up" assisting variable delivery fluid power supply.
The energy regenerating, load adaptive drive system of a wheeled vehicle can be still further modified to provide an optional mechanical connection of the engine shaft with the wheels of the vehicle. This optional mechanical connection can be used, for example, for long-distance driving.
The design of modified-integrated drive system may include an integrating mechanical transmission to select one of two alternative--component systems as follows:
Regenerative Adaptive Fluid Motor Control: The Energy Recuperating Pressure Drop Feedback Control System
A regenerative adaptive fluid motor control system having an independent regenerating circuitry (see FIGS. 11 to 22) is an integrated system incorporating only two major components:
The regenerative system having an independent regenerating circuitry is charactirized by that the primary and assisting supply line pressure drop feedback control systems are separated. On the other hand, the exhaust line pressure drop feedback control system (which can also be referred to as the energy recupturing pressure drop feedback control system) is shared between the two-way load adaptive fluid motor control system and the two-way load adaptive energy regenerating system. The energy recupturing pressure drop feedback control system includes an exhaust line energy recupturing means for varying a counterpressure rate in the exhaust power line and for recupturing a load related energy, such as a kinetic energy of a load mass or a compressed fluid energy of a fluid motor-cylinder. The energy recupturing pressure drop feedback control system and the exhaust line energy recupturing means can also be referred to as the energy recupturing pressure drop feedback control system and the exhaust line energy recupturing means, respectively.
Load Adaptive Energy Regenerating System
The above brief description of examplified load adaptive energy regenerating systems (see FIGS. 11 to 22) can be still further generalized and extended by the comments as follows.
3. As it was already mentioned before, the "exhaust fluid energy" of the exhaust fluid flow is understood as a measure of the load related energy being transmitted through the exhaust power line (that is line L3 or L5). The "exhaust fluid energy" can also be referred to as a "waste fluid energy", that is the energy which would be wasted unless regenerated.
5. The second load adaptive converting means include the assisting supply line pressure drop feedback control system and convert the accumulated energy of the energy accumulating means to an assisting pressurized fluid stream being implemented for powering the supply power line L2 of spool valve 2. The assisting pressurized fluid stream is actually generated by an assisting variable delivery fluid power supply which is included into the assisting supply line pressure drop feedback control system and which is powered by the energy accumulating means. The high energy-efficient, load adaptive process of converting the accumulated energy to the assisting pressurized fluid stream is facilitated by regulating the assisting supply fluid pressure drop across spool valve 2 by the assisting supply line pressure drop feedback control system and is basically controlled by the motor load. Note that the energy is being released by the energy accumulating means, while the motor load is positive (for example, during the acceleration of the motor vehicle).
6. Because the accumulation, storage, and release of the accumulated energy are all controlled by the motor load, the load adaptive energy regenerating system, as a while, is also basically controlled by the motor load.
Regenerative Adaptive Fluid Motor Control System
The above brief description of examplified regenerative adaptive fluid motor control systems (see FIGS. 11 to 22) can be still further generalized and extended by the comments as follows.
2. Note that assisting pressure rate P2R =P02 +ΔP2R of the assisting pressurized fluid stream is being correlated with the primary pressure rate P2 =P02 +ΔP2 of the primary pressurized fluid stream. Note also that ΔP2R >ΔP2 and, therefore, P2R >P2, while there is still any meaningful energy left in the energy accumulator.
4. Speaking more generally, it can be concluded that regeneration of a load related energy of the fluid motor and load means is accomadated by correlating the primary pressure rate of the primary pressurized fluid stream with the assisting pressure rate of the assisting pressurized fluid stream by regulating the primary supply fluid pressure drop across valve 2 and regulating the assisting supply fluid pressure drop across valve 2 by the primary supply line pressure drop feedback control system and the assisting supply line pressure drop feedback control system, respectively.
5. The exhaust line energy recupturing means of the energy recupturing pressure drop feedback control systems can be introduced by the exhaust line variable displacement motor 66--see FIGS. 11, 12, 16, 17, or by the exhaust line constant displacement motor 116 driving the exhaust line variable displacement pump 120--see FIGS. 18 to 22.
6. The assisting variable delivery fluid power supply, which is powered by the energy accumulating means, can be introduced by the assisting variable displacement pump 55--see FIGS. 11, 12, 16, 17, or by the assisting variable displacement motor 118 driving the assisting constant displacement pump 114--see FIGS. 18 to 21. The assisting variable delivery fluid power supply can also be introduced by the assisting constant displacement motor 198 driving the assisting variable displacement pump 194--as it is illustrated by FIG. 22.
7. The primary variable delivery fluid power supply can be introduced by the primary variable displacement pump 90--see FIGS. 12, 19, and 22 or by the variable speed primary motor (or engine) 92 driving the primary fluid pump--see FIGS. 11, 16, 17, 18, 20 and 21.
9. The variable displacement pumps having the built-in pressure drop feedback controllers are well known in the art. This type of control or the variable displacement pump is often called a "load sensing control" and is described in many patents and publications (see, for example, Budzich--U.S. Pat. No. 4,074,529 of Feb. 21, 1978). Moreover, the variable displacement pumps with the load-sensing pressure drop feedback controllers are produced (in a mass amount) by many companies which provide catalogs and other information on this load sensing control. Some of these companies are:
a) THE OILGEAR COMPANY, 2300 South 51st Street, Milwaukee, Wis., 53219, U.S.A. (see, for example, Bulletin 47016A);
b) SAUER-SUNDSTRAND COMPANY, 2800 East 13th Street, Ames Iowa 50010, U.S.A. (see, for example Bulletin 9825, Rev.E);
c) DYNEX/RIVETT, INC., 770 Capitol Driver, Pewaukee, Wis., 53072, U.S.A. (see, for example, Bulletin PES-1289).
Furthermore, the additional information of general nature on the feedback control systems and the hydraulic control system is also readily available from many publications--see, for example, the books already named above. In short, the load-sensing pressure drop feedback controllers of the variable displacement pumps are, indeed well known in the Art.
11. It is important to stress that load adaptive displacement means and the related pressure drop feedback control systems, made it possible to eliminate the need for any special (major) energy commutating equipment.
Load Adaptive Displacement Means and the Energy Regenerating Circle
Returning to FIG. 22, let's consider more specifically the load adaptive displacement means 196 of pump 194 and the load adaptive displacement means 130 of pump 120. The examplified schematics of load adaptive displacement means 196 and 130 are presented by FIGS. 23 and 24, respectively. These simplified schematics show:
FIGS. 23 and 24 are simplified and made similar to the extend possible. Each swashplate is driven by a plunger of the related cylinder against the force of a precompressed spring. Each hydraulic cylinder is controlled by the related three-way spool valve which is also provided with the pressure and tank lines. The pressure line is powered by an input pressure PIN which is supplied by any appropriate pressure sourse. The valve spool is driven by a pressure drop feedback signal against the force of the precompressed spring defining the pressure drop command signal. Note that three-way valve can also be replaced by a two-way valve which does not have the tank line (in this case the tank line is connected through a throttle valve to the line of hydraulic cylinder).
The assisting supply line pressure drop feedback signal P2R -P02 is applied to the spool 252 of valve 250 (see FIG. 23) to construct the assisting supply line pressure drop feedback control system and, thereby, to maintain pressure P2R =P02 +ΔP2R in the outlet line 30 of the assisting constant displacement motor 198 which is driving the assisting variable displacement pump 194 (as it was already basically explained before). At the balance of the assisting supply line pressure drop feedback control, the spool 252 of valve 250 is in the neutral spool position which is shown on FIG. 23. Note that ΔP2R >ΔP2, as it was already indicated before.
The exhaust line pressure drop feedback signal P05 -P5 is applied to the spool 272 of valve 270 (see FIG. 24) to construct the energy recupturing pressure drop feedback control system, and thereby, to maintain pressure P5 =P05 -ΔP5 in the exhaust line L5 powering the exhaust line constant displacement motor 116 which is driving the exhaust line variable displacement pump 120 (as it was already basically explained before). At the balance of the exhaust line pressure drop feedback control, the spool 272 of valve 270 is in the neutral spool position which is shown on FIG. 24. Note that pressure drop command signals ΔP2, ΔP2R, and ΔP5 are selected sot hat ΔP5 >ΔP2R >ΔP2, as it is required by expression (3).
FIG. 25 illustrates an examplified energy regenerating circle. It is assumed that the wheeled vehicle is moving in a horizontal direction only. As the vehicle is moving with a constant speed, decelerated, completely stopped, and accelerated, the related energy regenerating circle is completed. This stop-and-go energy regenerating circle has been already briefly introduced before (to explain the concept of preventing a substantial pressure drop regulation interferrence) and is easily readable on FIG. 25, when considered in conjunction with FIGS. 22 to 24 and the related text. For example, while the vehicle is decelerated, the swashplate 266 is positioned as indicated on FIG. 24. While the vehicle is accelerated, the swashplate 246 is positioned as indicated on FIG. 23.
Regenerative Drive System Having the Combined Energy Accumulating Means
The schematic shown on FIG. 19 is now further modified to replace the independent regenerating circuitry by the built-in regenerating circuitry and to improve the utilization of the combined energy accumulating means. Accordingly, the assisting variable delivery fluid power supply (motor 118 driving pump 114), the check valves 40 and 44, and the electrohydraulic energy converting means 142 are eliminated. The modified schematic is shown on FIG. 26. The added components are: (a) electrical motor-generator 290, (b) constant displacement motor 300, (c) shut-off valve 298, and (d) check valve 296. The primary engine (motor) 100, the direct-current motor-generator 290, the hydraulic motor 300, and the hydraulic pump 90 are all mechanically connected by a common shaft 98. The motor-generator 290 is also electrically connected (through lines 292 and 294) with the electrical accumulator 144. On the other hand, the hydraulic accumulator 122 is hydraulically connected (through shut-off valve 298) with the inlet line 302 of motor 300.
The regenerative drive system of FIG. 26 makes it possible to minimize the required engine size of a wheeled vehicle. The engine 100 is provided with a speed control system which is assumed to be included in block 100 and which is used to maintain a preselected (basic) speed of shaft 98 while allowing some speed fluctuations under the load which is applied to the shaft 98. The related margin of accuracy of the speed control system is actually used to maintain a balance of power on the common shaft 98 and, thereby, to minimize the required engine size of a wheeled vehicle.
The driving torque of shaft 98 is generally produced by engine 100, by motor-generator 290 (when it is working as a motor), and by motor 300 (when it is powered by the hydraulic accumulator 122 through shut-off valve 298). The loading torque of shaft 98 is basically provided by pump 90 and by motor-generator 290 (when it is working as a generator). Note that at some matching speed of shaft 98 (within the margin of accuracy of the speed control system) a speed-dependent voltage of generator 290 is equal to a charge-dependent voltage of accumulator 144, so that no energy is transmitted via lines 292 and 294. As the speed of shaft 98 is slightly reduced, the electrical energy is transmitted from the electrical accumulator 144 to the electrical motor 290 helping engine 100 to overcome the load. On the other hand, as the speed of shaft 98 is slightly increased, the electrical energy is transmitted from the electrical generator 290 to the electrical accumulator 144, allowing to utilize the excess power of shaft 98 for recharging the electrical accumulator 144. Note also that shut-off valve 298 is normally closed and is open only under some preconditions--in order to power the constant displacement motor 300 by the hydraulic energy of accumulator 122. Let's assume, first, that a wheeled vehicle, such as a city transit bus, is moving in a horizontal direction only. And let's consider briefly the related energy regenerating circle.
An optional control signal "S" which is applied to the shut-off valve 298, is produced by an optional control unit which is not shwon on FIG. 26. This control unit can be used for controlling such optional functions as follows:
Two Basic Types of Regenerative Systems
There are basically two types of regenerative adaptive fluid motor control systems: (a) the regenerative system having an independent regenerating circuitry (see FIGS. 11 to 22) and (b) the regenerative system having a built-in energy regenerating circuitry (see FIGS. 9, 10, and 26). The first type of regenerative systems is identified by that the primary and assisting supply line pressure drop feedback control systems are separated. The second type of regenerative systems is identified by that the primary and assisting supply line pressure drop feedback control systems are not separated and are represented by only one supply line pressure drop feedback control system. The generalized first-type systems have been already introduced by FIGS. 13, 14, and 15. A generalized second-type system is shown on FIG. 27, which is mostly self-explanatory and is still further understood when compaired with FIGS. 9, 10, 26, and 15.
Adaptive Fluid Control and the Load Environments
It is understood that this invention is not limited to any particular application. It is to say that FIGS. 1, 4, 9, and 12, are not related only to the hydraulic presses. It is also to say that FIGS. 10, 11, 16 to 22, and 26 are not related only to the motor vehicles. In fact, the typical adaptive schematics which are shown on FIGS. 1, 4, 6, 9 to 12, 16 to 22, and 26 are exclusively associated only with a type of motor load of the fluid motor 1 (or 150), as it is characterized below:
(a) the schematics shown on FIGS. 1, 4, 9, and 12 are adaptive to the one-directional static load force;
The above load-related simplified classification of typical adaptive schematics is instrumental in modifying these schematics for the modified load environments. For example, the schematic shown on FIG. 18 is adaptive to the two-directional dynamic load force, which is generated during acceleration and deceleration of a load mass moving only in one direction. If the load environments are modified by replacing this two-directional dynamic load force by the one-directional static load force, the schematic of FIG. 18 must also be modified. The modified schematic may include the five-way spool valve 2 instead of the four-way spool valve 2 which is shown on FIG. 18. In this case, the energy regenerating circuitry using hydraulic accumulator 122 must be switched over from the exhaust power line L5 to the exhaust power line L3, as it is illustrated by FIG. 12--for a case of using the fly wheel accumulator 94.
Adaptive Fluid Control with a Supplementary Output Motor
There is one special modification of independent regenerating circuitry which is not covered by the generalized schematic of FIG. 15 and which, therefore, is considered below. The regenerative braking pump 170 of FIG. 21 can also be used as a variable displacement motor to make-up a supplementary variable displacement motor/pump. The pump functions of this supplementary output motor/pump have been already studied with the help of FIG. 21. For simplicity, the motor functions of this supplementary output motor/pump will also be studied separately.
FIG. 28 is derived from FIG. 21 by replacing the supplementary output pump 170 by the supplementary output motor 170 and by eliminating the assisting supply line pressure drop feedback control system (including motor 114 and pump 118) and some other components (check valves 40, 44, and 174). The variable displacement motor 170 is powered by the hydraulic accumulator 122 through a shut-off valve 297 which is basically controlled by pressure signal P02. While this pressure signal is comparatively small, the shut-off valve 297 is closed. As signal P02 is further raising-up, the shut-off valve 297 is open, provided that there is still enough energy stored in the hydraulic accumulator 122.
The variable displacement means 99 of motor 170 are constructed to make-up a displacement feedback control system including a variable displacement mechanism (of motor 170) and employing a displacement feedback control errow signal Δd. This errow signal is generated in accordance with a difference between a command-displacement signal do =Cp �P02 (where Cp is a constant coefficient) and a mechanism displacement (feedback signal) d1 of the variable displacement mechanism of motor 170. A pressure-displacement transducer converting the pressure signal P02 into the proportional command-displacement signal do =Cp �P02 is included into the variable displacement means 99 of motor 170. This transducer may incorporate, for example, a small spring-loaded hydraulic cylinder actuated by the pressure signal P02. The displacement feedback control errow signal Δd=do -d1 is implemented for modulating the variable displacement mechanism of motor 170 for regulating the mechanism displacement d1 of the variable displacement mechanism of motor 170 in accordance with the command signal do (and hence, in accordance with the pressure rate P02 =do /Cp in the motor line L1). It should be emphasized that the displacement feedback control system, which is well known in the art, is, in fact, the position feedback control system and that, therefore, the general position feedback control technique, which is characterised above with respect to the fluid motor position feedback control system, is also basically applicable to the displacement feedback control system.
In general, the displacement feedback control circuitry of motor 170 is adjusted so that, while the pressure P02 in the motor line L1 is comparatively low, this circuitry is not operative and d1 ≅0. As the pressure P02 in the motor line L1 is further raising-up, the displacement d1 of motor 170 is increasing accordingly, so that the total accelerating torque is properly distributed between the fluid motor 1 and the supplementary motor 170. The use of motor 170 makes it possible to substantially increase the available (total) accelerating torque of the wheeled vehicle.
The related generalized schematic of FIG. 29 is derived from FIG. 15, is most self-explanatory, and is reflective of the facts that the assisting supply line pressure drop feedback control system is now eliminated and that pressure Pac from the hydraulic accumulator 122 is now applied to the supplementary output motor 170 of the fluid motor and load means.
Some Other Related Considerations
The schematic of FIG. 26 can be modified by changing the hybrid motor means driving pump 90. The examplified modifications are as follows.
1. The electrical motor-generator 290 and the related electrical accumulator 144 are excluded from this schematic. The constant displacement motor 300 is replaced by a variable displacement motor which is used to construct a supplementary shaft-speed feedback control system maintaining the preinstalled speed of shaft 98 when this variable displacement motor is powered by accumulator 122. As a result, the hydraulic energy of accumulator 122 is transmitted to shaft 98 in accordance with the actual energy requirement. Note that possible interference between the main shaft-speed feedback control system (of primary engine 100) and the supplementary shaft-speed feedback control system (of the variable displacement motor) is prevented by providing
ΔV--is a sufficient velocity margin between these two systems. In other words, the supplementary speed control system should actually be regulated just "slightly above" the main speed control system.
2. The primary power line 54 (see FIGS. 11 to 22) can be protected by the maximum pressure relief valve. The maximum pressure in line 54 can also be restricted by using the variable delivery means 93 of pump 90. In general, the maximum pressure relief valves can also be used to protect other hydraulic lines.
Regenerative Adaptive Fluid Control Versus Non-regenerative Adaptive Fluid Control
As it was already mentioned before, there are basically two types of the two-way load adaptive fluid motor control systems. The non-regenerative adaptive fluid motor control systems are equipped with an exhaust line pressure drop feedback control system including an exhaust line pressure drop regulator. On the other hand, the regenerative adaptive fluid motor control system are equipped with an energy recuperating pressure drop feedback control system including an exhaust line energy recuperating means.
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