Electrohydraulic servo drive and hydraulic amplifier

Description Field of the Invention

The group of inventions relates to the sphere of machine building and can be used in systems of control of actuators of a variety of machines when power consumption is limited, in particular the hydraulic amplifier is intended for use in the electrohydraulic servo drive of throttling-displacement regulation.

Prior Art An electrohydraulic servo drive is known from the published patents containing a two-cascade hydraulic amplifier, a hydraulic servo motor, a hydrocontrolled pump, a power limiter, an elecromechanical transducer controlling the throttle of the first cascade of the hydraulic amplifier rigidly connected to the second cascade distributor made with two lines communicating with the hydraulic motor ends, and two hydraulic lines communicating with the pressure and suction ends of the pump, the hydraulic amplifier containing a fixed cartridge, a movable bushing and a cylindrical valve with serially arranged operating collars in the larger diameter port in the cartridge (1). The drawbacks of these drives and the hydraulic amplifiers are large overall dimensions and mass, poor efficiency, intricacy of manufacture and technical maintenance, insufficient range of transmitted frequencies of control signals that can be processed with sufficient accuracy, poor dynamic stability and low quality of the transition process due to the non-optimal schematic and design parameters.

Another electrohydraulic servo drive for throttling-and-displacement regulation is known from the published patents containing a two-cascade hydraulic amplifier (a hydrodistributor) and its body contains a controllable pump, a compensating pressure-makeup device, a hydraulic motor, a fluid makeup valve, a safety valve, a reduction valve, the hydraulic amplifier containing an integrated service valve installed in the bushing with a

partitioning on the outer surface, its central ports through one are divided by a partition forming two chambers with the body, one communicating with the pressure line and the other with the command chamber of the servo piston connected by mechanical, electrical and hydraulic links, the cradle in which an axial plunger or an axial piston pump is installed being pivoted from one side on the cylindrical plunger of the servomechanism through an axial longitudinal rectangular slot, and from the other side being pivoted through a pusher and spring-loaded through the angle of maximum efficiency, the control chamber of the servomechanism through the central groove in the power limiter is made as a spring-loaded double-operating collar slide valve capable to shut off the central groove from the control chamber of the hydraulic amplifier and communicating through the safety valve edge with the drain, communicating with two control ports in the hydraulic c amplifier. (2).

The drawbacks of these drive and hydraulic amplifier are poor efficiency due to insufficient effectiveness of control of the pump's performance, high complexity of fabrication and maintenance, particularly the filling of the drive circuit and the hydraulic amplifier chamber with the pressure fluid, insufficient range of frequencies of control signals that can be executed with sufficient accuracy, poor quality of the transitional process and low dynamic stability due to the non-optimal circuit and design parameters, including lack of any position feedback circuit with the required coefficient of amplification and uncertainty of ratios of throats and flow areas.

Summary of the Invention The technical task of this group of inventions combined by a common invention idea is to develop an effective electrohydraulic servo drive of throttling-and-displacement regulation and an effective hydraulic amplifier.

The technical result of the group of inventions is improvement of the efficiency, simplification of fabrication and maintenance, expansion of the range of transmitted frequencies, improvement of dynamic characteristics, vis. the stability margin and quality of the transitional process.

The nature of the invention is that it contains a hydraulic motor, a pump with a two-line hydraulic control and spring-loaded in the direction of maximum flow rate, a reduction valve, a two-cascade hydraulic amplifier with a controllable throttle of the first cascade, and a self-aligned five-line distributor of the second cascade, a three-line power limiter, a compensating pressure makeup device with its piston chamber communicating with the pump's suction end, filling valves and a hydraulic motor displacement sensor connected to one input of the comparator, its output via the amplifier is connected to an electromechanical converter controlling the throttle of the first cascade of the hydraulic amplifier rigidly connected to the amplifier of the second cascade with two hydraulic lines that communicate with the hydraulic motor chamber, with one hydraulic line communicating with the three-line power limiter and two hydraulic lines communicating with the pressure and suctions ends of the pump, and two control chambers having the effective flow areas with the ratios within 1.55í1.65, the chamber with the larger flow area communicating with the inlet of the controllable throttle of the first cascade, the chamber with the smaller flow area communicating with the outlet of the reducing valve connected to the stem chamber in the throtting- and-desplacement regulator and through the first throttle of constant cross- section with the outlet of the controllable throttle of the first cascade, the outlet of the reducing valve communicating with the pump pressure chamber, the hydraulic line of the five-line distributor connected to the three-line power limiter and communicates with its control chamber through one of its hydraulic lines, and though the second throttle of constant cross-section with its hydraulic line connected to the pump control chamber operating in the direction of a larger flow rate, the third hydraulic line of the three-line power limiter communicates with the pump suction end, while its other control chamber operating in the direction of reducing the flow rate and communicating with the pump pressure end. It is preferable that the feedback sensor is connected to the hydraulic motor with a pinion-rack drive, at the same time the five-line distributor is designed so that it can control the delivery by the pump and the throttling

regulation of the hydraulic motor by connecting all the hydraulic lines together in the neutral position, and when it displaces from the neutral position it produces controllable throttles for connecting one end of the hydraulic motor with the suction side and the other end with the pressure side of the pump simultaneously communicating with the controllable throttle connected to the three-line power limiter capable of controllable connection of this hydraulic line with the pump control chamber and disconnection if pressure leaps in these hydraulic lines, and to connect them simultaneously through the second throttle of constant cross-section and the pump control chamber with its suction side if pressure leaps still more. At the same time, the effective flow area of the control chamber of the three-line power limiter is 0.24í0.26 of the effective flow area through the control chamber of the five-line distributor with the least effective flow area, the first throttle of constant cross- section has the open flow area 0.28í0.32 of the maximum open flow area through the controllable throttle of the first cascade, one filling valve communicates with the hydraulic line of the five-line distributor connected to the three-line power limiter, and the second with the pump suction side through an additionally installed fluid makeup valve.

The nature of the invention in relation to the hydraulic amplifier is that it contains a fixed cartridge, a movable bushing and a cylindrical valve with three serially arranged operating collars located in the larger diameter port in the cartridge, an intermediate collar in the smaller diameter port in the cartridge , and a longitudinal guide carrying the bushing, meanwhile the valve is installed so that it forms control chambers in the cartridge, one chamber locates from the free endface of the sidemost operating collar and communicates with a blind longitudinal channel in the valve , another chamber through the throttle port of smaller diameter communicates with the second control chamber formed around the intermediate collar and the next adjacent operating collar, while the throttle port of larger diameter communicates with the surface of the guide carrying the movable bushing producing the controllable throttle of the first cascade, meanwhile the hydraulic amplifier has five external hydraulic lines of the second cascade,

and the cartridge has five outer circular grooves, the first and the fourth communicating with one external hydraulic line and with the bore in the cartridge through ports forming together with the sidemost collars the valve controllable throttles, the second and third communicating with two external hydraulic lines and with the inner bore in the cartridge, the fifth with the said control chamber formed around the intermediate collar, at the same time the outer separated grooves are arranged equispaced over the circumference between the second and third grooves in the cartridge, two of them communicate with one external hydraulic line, two others with the other external hydraulic line, and they communicate in pairs with the inner bore in the cartridge separated by ports forming controllable throttles with the central collar.

It is preferable that the control chamber located from the side of the free endface of the sidemost operating collar is provided with a larger effective flow area, while the control chamber formed around the intermediate collar at the other sidemost operating collar is provided with a smaller effective flow area with the ratio beteen the effective flow areas being within 1.55í1.65, the first and fourth outer circular grooves in the cartridge communicate with the inner groove in the cartridge through rectangular ports, the second and third through round ports, while the outer grooves of rectangular cross-section communicate through rectangular ports, at the same time the fifth circular groove communicates with the control chamber through six inclined holes, the throttle port of smaller diameter has the open flow area 0.28í0.32 of the maximum open flow area of the throttle port of a larger diameter that is made diametrical and communicates with the circular groove on the surface of the guide, while the guide has several blind grooves on its outer surface .

Detailed Description of the invention

Fig. 1 shows the schematic diagram of the electrohydraulic servo drive, Fig. 2 - the design diagram of the hydraulic amplifier, Fig. 3 - the cartridge of the second cascade of the hydraulic c amplifier, Fig. 4 - the section A-A in

Fig. 3, Fig. 5 - the movable bushing first of the cascade of the hydraulic

amplifier, Fig. 6 - the right-side elevation of Fig. 5, Fig. 7 - the valve of the hydraulic amplifier, Fig. 8 - the logarithmic amplitude-frequency characteristics of the open drive under nominal loading, Fig. 9,10 - the transitional characteristics of the drive and its links when idling and at nominal loading, respectively.

The electrohydraulic servo drive comprises servo hydraulic motor 1 , pump 2 with double-sided hydraulic control and spring 3 acting on pump regulating member 2 towards the maximum flow rate through pump 2, reduction valve 4 with adjusting throttle 5, two-cascade hydraulic amplifier 6 with adjusting throttle 6 of the first cascade and self-aligning five-line distributor 7 of the second cascade, three-line power limiter 8, piston pressure makeup (accumulating) compensator 9, piston chamber 2 communicating with the pressure side of the pump, filling valves 10, 11 and sensor 12 of displacements of hydraulic motor 1. Hydraulic motor 1 has chambers and a reversible movable member, a stem, or a shaft (not designated). Sensor 12 is linked to hydraulic motor 1 with a pinion-rack gear (not designated) with 31 teeth. Pump 2 has a drive motor (omitted) and a regulating member, such as a plunger rotating the inclined disk (omitted), in this case chambers 28, 30 are located along the plunger endfaces. Sensor 12 is connected to an input of comparator 13, its output is connected through amplifier 14 and air-tight input (hermetized inlet) with electromechanical converter 15 controlling throttle 6 of the first cascade of the hydraulic amplifier rigidly secured to distributor 7 of the second cascade. Distributor 7 is provided with two hydraulic lines 16, 17 communicating with the chambers of hydraulic motor 1 , with one hydraulic line 18 that communicating with three-line power limiter 8, two hydraulic lines 19,20 communicating with the suction and pressure sides of pump 1 , and with two control chambers 21 , 22 having a preset ratio between the effective flow areas below. Chamber 22 with the larger flow area communicates with the inlet of controllable throttle 6 of the first cascade, while chamber 21 with the smaller flow area communicates with the inlet of reducing valve 4 communicating with the stem chamber of compensating pressure makeup device 9 and through first

throttle 23 of constant cross-section with the inlet of controllable throttle 6 of the first cascade. At the same time, the inlet into reducing valve 4 communicates with the pressure chamber of pump 2, hydraulic line 18 of the five-line distributor connected to three-line power limiter 8 communicates 5 with control chamber 24 of the latter, with its hydraulic line 25 and through second throttle of 26 constant cross-section with another hydraulic line 27 and farther communicating with control chamber 28 of pump 2 acting towards increasing its flow rate, third hydraulic line 29 of three-line power limiter 8 communicates with the suction chamber of pump 2, its other control chamber

10 30 acts towards reducing the flow rate and communicates with the pump's its pressure chamber.

Five-line distributor 7 is made so that it can control the delivery by pump 2 and throttling control of hydraulic motor 1 by interconnecting in the neutral position all hydraulic lines 16,17,18,19,20, and during displacement away

15 from the neutral position to form controllable throttles to connect one the chambers of hydraulic motor 1 with the suction chamber and the other with the pressure chamber in pump 2 and simultaneously connect the controllable throttle to the hydraulic circuit with the amplifier through hydraulic line 18 communicating with the three-line power limiter capable to adjust 0 communication along this hydraulic circuit with line 18, with control chamber 28 of pump 2, it closes connection in case pressure increases in hydraulic line 18 and simultaneously opens through second throttle 26 of constant cross-section and connects control chamber 28 of pump 2 with its suction side if pressure in hydraulic line 18 becomes still higher. 5 The effective flow area of control chamber 24 of three-line power limier

8 (the area of the circumference with the diameter 4 mm, for instance) is 0.24í0.26 of the effective flow area of control chamber 21 of five-line distributor 7 with a smaller effective flow area (the area of the ring with the outer and inner diameters equal, for instance, to 11 mm and 7.5 mm, 0 respectively).

First throttle 23 of constant cross-section has the open flow area (for instance, 0.7 mm in diameter) that makes up 0.28í0.32 of the maximum

open flow area (for instance, 0.9 mm in diameter) of controllable throttle 6 of the first cascade.

Filling valve 10 communicates with hydraulic line 18 of five-line distributor 7 and with hydraulic line 25 of three-line power limiter 8, while second valve 11 communicates with the suction end of pump 2 through additional pressure makeup valve 31.

The hydraulic amplifier comprises fixed cartridge 32, movable bushing 33 and the cylindrical valve with three serially arranged operating collars 34, 35, 36 located in the port of a larger diameter in the cartridge 32 form distributor 7, intermediate collar 37 located in the port of the smaller diameter in cartridge 32, and longitudinal guide 38 carryes bushing 33. Bushing 33 is made thin-walled with the minimal possible weight (1-2 g).

Hydraulic lines 16-20 of distributor 7 are external hydraulic lines of the hydraulic amplifier. The valve is installed so that it produces control chambers 21 , 22 in cartridge 32. Chamber 22 is on the side of the free endface of sidemost operating collar 36 and it communicates with blind longitudinal channel 39 in the valve and farther with first throttle 23 of constant cross-section made as a throttling port of smaller diameter (0.7 mm) and communicating with second control chamber 21 round intermediate collar 37 adjacent to operating collar 34, while throttling port 40 of larger diameter (0.7 mm) communicates with the surface of guide 38 carrying movable bushing 33 that forms with the edge of controllable throttle 6 the first cascade of the hydraulic c amplifier. The hydraulic amplifier has five external hydraulic lines 16-20 (Fig. 1) of the second cascade. Cartridge 32 is provided with five outer circular grooves 41-45, among them first and fourth grooves 41 ,44 communicate with one external hydraulic line 20 and the internal bore in cartridge 32 with ports 46,47 forming sidemost collars 34,36 of the valve controllable throttles, second and third grooves 42,43 communicate with two external hydraulic lines 16,17 and they communicate with the internal bore in cartridge 32, while groove 45 communicates through reduction valve 4 with the pressure side of pump 2 and with said control chamber 21 around intermediate collar 37. Over the circumference, there are equispaced.

Individually separated outer grooves 48, 49, 50, 51 of rectangular cross- section between second and third grooves 42, 43 in cartridge 32. Groves 48- 51 do not intersect and portions of the outer surface of cartridge 32 separate them. Two grooves 48, 50 communicate with one external hydraulic line 19, while two other grooves 49, 51 with another external hydraulic line 18 and the inner bore in cartridge 32 with isolated rectangular ports 52, 53, 54, 55 connect them in pairs forming controllable throttles with central collar 35.

Control chamber 22 from the free endface of sidemost operating collar 36 has a larger effective flow area, while control chamber 21 around intermediate collar 37 at another sidemost operating collar 34 has a smaller effective flow area, with the ratio between their effective flow areas being within 1.55í1.65 (the dimensions are indicated above).

First and fourth outer circular grooves 41 ,44 on cartridge 32 communicate with the inner bore in cartridge 32, with rectangular ports 46, 47, second and third grooves 42,43 communicating with round ports 56, while outer grooves 48 - 51 of rectangular cross-section communicate with rectangular ports 52-55, at the same fifth circular groove 45 of cartridge 32 communicates with control camber 21 through six inclined holes 57. Collars 34, 35 are made with negative overlap, while collar 36 with positive overlap of the ports in cartridge 32.

The throttling port of smaller diameter, 0.7 mm, for instance, of throttle 23 has the radial open flow area making up 0.28í0.32 of the maximum open flow area of throttling port 40 of larger diameter, 0,9 mm, for instance, that is provided with a diametric hole and it is connected by circular groove 58 on the surface of guide 38 forming throttle 6 of the first cascade with the endface edge of bushing 33.

Guide 38 is made with several blind grooves 59 on the outer surface carrying bushing 33 that has truncated conical projection 60 with the angle at the apex 22° for meshing with electromechanical converter 15. The amplitude-frequency logarithmic characteristic is designated IWGw)I in Fig. 8, the phase-frequency logarithmic characteristic is designated Arg W(Jw), the phase margin is designated "δ". The characteristics of the

transitional process have the following designations in Fig. 8, 10: "a" - the rectangularly shaped input signal at the positive input of the comparator, "b" - the stroke of the hydraulic motor, "c" - the speed of the hydraulic motor, «d" - the stroke of the valve of the distributor, «e" - the stroke of the regulating member of the pump, T - the delivery pressure of the pump.

The electrohydraulic servo drive and the hydraulic amplifier operate in the following manner.

The drive circuit is filled through valves 10, 11 that are arranged in the above-said manner in order to ensure guaranteed filling of all cavities and chambers and full elimination of air.

When the drive is idle, there is no delivery pressure, spring 3 of the regulating member (the inclined washer, etc.) of pump 2 occupies the position of the maximum stroke of plungers (or pistons), i.e. the position of the maximum operating fluid flow rate. The pressure in chambers 28, 30 and in chambers 21 , 22 coincides. When pump 2 starts, the delivery pressure in chamber 30 rises moving the regulating member of pump 2 into the position of the minimum operating fluid flow rate necessary to make the drive and the hydraulic amplifier ready to process the control signal. Therefore, when no control signal arrives at the positive input of comparator 13, the energy consumption is minimum. Reduction valve 4 establishes and afterwards maintains stable pressure in grove 45 in cartridge 32, i.e. at the outlet from throttle 23, in chamber 21 of the hydraulic amplifier and in stem chambers of pressure compensator 9 maintaining the necessary level of pressure at the inlet into valve 31 , hence at the suction side of pump 2. The position of the edge of the endface of bushing 33 in respect to the edges of groove 58 maintains the condition (resistance) of throttle 6 necessary for the equilibrium of the valve of distributor 7 of the hydraulic amplifier in the neutral position.

When the outputted control signal "a" arrives at the positive input of comparator 13, this signal is converted by amplifier 14 and arrives to electromechanical converter 15 that moves bushing 33 over surface 38 and thus changes the resistance of throttle 6 of the first cascade of the hydraulic amplifier. Thus, the pressure in chamber 21 is determined by the adjustment

of reducing valve 4, while in chamber 22 by the resulting total resistance of throttles 6 and 23. As a result, working pressure drop appears in chambers 21 , 22 and the force determined by the ratio between the effective flow areas and pressures in these chambers that acts on the valve of distributor 7 that moves in the direction of the resulting force. Displacement of the valve changes the resistance of the controllable throttles formed by collars 34-36 of the valve through ports 46, 47, 52-55 and 56 cartridge 32. The displacement (stroke) "d" of the valve of distributor 7 at selected ratios of the effective flow areas in chambers 21 , 22 takes place smoothly and no oscillations accompany it (Fig. 9,10).

Simultaneously with the valve's displacement the position of bushing 33 is restored in respect to grooves 58 and port 40, therefore, the initial resistance of throttle 6 and the valve equilibrium are restored. The valve moves into the position determined by the value of the signal to electromechanical converter 15.

As a result, a pressure drop appears in hydraulic lines 16, 17 and in the chambers of hydraulic motor 1. Concurrently pressure is delivered along hydraulic lines 18, 25, 27 into chamber 28, as a result the regulating member of pump 2 displaces into the position of the preset flow rate into hydraulic motor 1. Unlike the analogs, the displacement (stroke) «e" of the regulating member of pump 2 takes place smoothly and no oscillations accompany it, while changes "f" in the pressure in pump 2 are characterized by quickly attenuating oscillations of a small amplitude that induce no vibrations in the drive movable links and their magnitude is tolerable, i.e. they require no reinforcement of the design in order to withstand a single maximum pressure leap (Fig. 9, 10).

The operating fluid is delivered into one of the chambers of hydraulic motor 1 and hydraulic line 18 under pressure dictated by the loading and it is formed from another chamber on the suction side of pump 2. Hydraulic motor 13 determines the operating fluid flow rate through pump 2. There is no re-adjustment of displacement "b" of hydraulic motor 1 , its speed "c" changes smoothly, specifically under load. The transitional process, since the

control signal begins, lasts minimal time until the steady mode of displacement of hydraulic motor 1 is achieved because it does not exceed the time of displacement of the regulating links (the valve and the regulating member of pump 2), i.e. it is shorter than that of the analogs (Fig. ,10). Displacement of hydraulic motor 1 under load is controlled by sensor 12 that registers the displacement with the help of a clearance-free pinion-rack gear. Sensor 12 shapes a negative feedback signal by the position that is added by device 13 algebraically to the control signal. The signal at the output of device 13 and amplifier 14 reduces to zero, electromechanical converter 15 resumes the initial position returning bushing 33, and therefore the resistance of throttle 6 and distributor 7 to their initial positions, the valve of the distributor occupies the initial position in respect to cartridge 32. The pressure in hydraulic lines 16, 17 and chambers of hydraulic motor 1 equalizes. Hydraulic line 18 receives no pressure; hence, the pressure in chamber 28 of pump 2 drops correspondingly, its regulating member returns into the position of the minimal capacity.

The drive circuit has the phase margin δ equal to 60 degrees at the cutoff frequency 16 Hz (Fig. 8) that guarantees prevention of auto- oscillations. Under the loading to which the characteristics in Fig. 8-10 are adjusted, the amplification coefficient can grow until it reaches the cutoff frequency 80 Hz (at a zero phase margin). When the loading in hydraulic motor 1 reduces correspondingly, the amplification coefficient can grow, while the cutoff frequency can reach 150 Hz.

The preset loading on hydraulic motor 1 determines tolerable pressure in pump 2, therefore the value of tolerable power consumed by the drive and proportional to the product of the values of pressure drop and flow rate through pump 2. In case of unauthorized loading increase in hydraulic motor 1 and delivery pressure in pump 2, the pressure grows simultaneously in hydraulic line 18, 25 and chamber 24 of limiter 8. The latter regulates power by the pressure in chamber 24, for that it moves in the direction of reduction of the passage cross-section connecting hydraulic line 25 with hydraulic line 27 and reducing the pressure in chamber 28 of pump 2 and

its flow rate drops too. In case of further pressure growth, limiter 8 disconnects hydraulic line 25, 27, then chamber 28 communicates with hydraulic line 18 only through throttle 26, the flow rate through pump 2 drops to the value close to the minimal. If the delivery pressure continues to grow, limiter 8 connects hydraulic line 27 to hydraulic line 29, i.e. with the suction side, the pressure in chamber 28 becomes minimal possible, the regulating member of pump 2 returns into the position of the minimal delivery and it (the flow rate) in pump 2 reduces to the minimal possible when the motor is running. Thus, concurrent volume regulation of the pump with chambers 28,30 and the throttling control with the controllable throttles of the first and second cascades of the hydraulic amplifier and simultaneous processing of the feedback with the pinion-rack gear between hydraulic motor 1 and sensor 12 ensures higher efficiency of the drive. The optimal arrangement of the filling valves in respect to the hollows and chambers of the drive simplifies fabrication and maintenance of the drive. The optimal ratios between the effective flow areas of the control chambers and throttling ports expands the range of transmitted frequencies, improves the dynamic characteristics, such as the stability margin and the quality of the transitional process.

Industrial Applications

The present invention is embodied with multifunctional and easily available state-of-the-art equipment and substances extensively used in machine building and health care to produce hydraulic equipment and means of its automatic control.

Information sources

1. US Patent # 3095906, 1963.

2. RU Pantent # 2218486, 2003, (prototypes).