High-efficiency continuous rotating hydraulic joint and control system

Abstract

A high-efficiency continuous rotating hydraulic joint and a control system comprise a swash plate mechanism used for driving the joint to rotate, the swash plate mechanism comprises a swash plate and a power output shaft, and the swash plate is driven by a plurality of multi-cavity hydraulic cylinders to achieve forward and reverse rotation of the power output shaft. The multiple multi-cavity hydraulic cylinders are evenly distributed below the swash plate with the power output shaft as the center, composite piston rods of the multi-cavity hydraulic cylinders and the power output shaft are distributed in parallel, the jacking ends of the composite piston rods are connected with ball bearing seats through ball bearings, and the jacking ends of the composite piston rods are assembled on the swash plate in a sliding mode through the ball bearing seats. The control system comprises an inner ring control system and an outer ring control system, different load matching control methods are adopted corresponding to different rotation angle positions of the power output shaft, fine adjustment of the proportional throttle valve is combined, high-precision constant torque control of the device in a continuous rotation motion state can be achieved, and the device is high in reliability and high in reliability. And high-precision variable-torque control can be realized to match the variable load torque.

Description

Technical Field

[0001] The invention relates to the field of hydraulic transmission drive, and in particular to a high-efficiency continuous rotating hydraulic joint and a control system. Background Art

[0002] The existing hydraulic drive methods for legged robots and multi-joint mechanical arms include linear hydraulic cylinders, swing hydraulic cylinders and cycloidal motors. Linear hydraulic cylinders are the most commonly used actuators in hydraulic joint drives due to their simple structure, light weight and reliable operation.

[0003] Linear hydraulic cylinders are not conducive to the integration and miniaturization of joint drives. The additional connecting rod mechanism increases the inertial mass, nonlinearity of the driven joint and the weight of the entire drive device, which adds difficulties to the joint control and lightweight design of the robot.

[0004] The swing hydraulic cylinder can be directly installed at the joint as a drive device, but its structure is too complicated, the mass is large, and the size along the rotation axis is large.

[0005] Compared with other hydraulic motors, the cycloid motor is small in size and light in weight, but its large internal leakage leads to low efficiency and difficulty in achieving high-precision position and torque control.

[0006] The linear hydraulic cylinders, swing hydraulic cylinders and cycloidal motors commonly used in multi-joint hydraulic drives have problems such as low integration and modularization, large size and high quality. In addition, there is an important problem, which is extremely low efficiency. The main reasons for the low efficiency are as follows: Due to weight and volume limitations, hydraulic drives for multi-joint mechanical structures generally adopt a single pump source-multiple actuator system structure, such as Fig. 9 As shown, P s and Q s is the output pressure and flow rate of the pump source, P n and Q n Respectively n For the various types of hydraulic actuators commonly used above, since their effective action area is fixed, the load pressure can only be adjusted through the throttle valve. P n , so that the output force of the hydraulic actuator matches the load force. If the load variation of a single joint is large or the load difference between different joints is large, the load pressure P n The change is large, different load pressure P 1 ~ P nThe difference is large, the oil source pressure P s And each load pressure P n The difference between them will be large, and the throttling power loss of the throttle valves on each branch will be large, resulting in very low efficiency of the entire system. The BLEEX exoskeleton hydraulic drive system funded by the US Defense Advanced Research Projects Agency has been reported to have an efficiency of only 14%. Dr. Zhang Yanting of Zhejiang University's doctoral thesis "Energy Saving Research on Hydraulic Excavators Based on Hybrid Power and Energy Recovery" shows that the efficiency of an excavator using a single pump source-multi-actuator hydraulic drive system is only 40%; The existing patent number is: CN201610361855.6, and the patent name is: The invention patent of multi-chamber hydraulic cylinder and its control system and control method discloses a multi-chamber design of a hydraulic cylinder. By selecting different cavities to be connected to the high-pressure oil circuit or to the low-pressure oil circuit, the oil source pressure and the load pressure are matched, thereby ensuring the compact structure and improving the efficiency of the hydraulic system. However, how to apply this multi-chamber hydraulic cylinder to the hydraulic joint actuator, and how to provide a hydraulic joint actuator with high integration and modularity, small size, light weight, and efficient drive, are technical problems that need to be solved urgently. Summary of the invention

[0007] The present invention solves the deficiencies of the prior art and provides a high-efficiency continuous rotating hydraulic joint and control system that realizes high-efficiency driving under variable load power through a multi-cavity structure, converts the linear motion of a linear hydraulic cylinder into rotary motion through a rotating swash plate mechanism, and realizes highly integrated structure and high-precision control of joint position and torque. The present invention can be used in the joint drive of various engineering machinery operating mechanical arms and various multi-joint robots to improve the power density and driving efficiency of the joint.

[0008] The present invention includes a high-efficiency continuous rotating hydraulic joint, including a rotating swash plate mechanism as a driving joint rotation, the rotating swash plate mechanism includes a swash plate and a power output shaft, the swash plate is driven by a plurality of multi-chamber hydraulic cylinders to realize positive and negative rotation of the power output shaft, the plurality of multi-chamber hydraulic cylinders are evenly arranged below the swash plate with the power output shaft as the center, the composite piston rod of the multi-chamber hydraulic cylinder is arranged parallel to the power output shaft, the lifting end of the composite piston rod is connected to the ball bearing seat through a ball bearing, and the lifting end of the composite piston rod is slidably assembled on the swash plate through the ball bearing seat.

[0009] In the above embodiment, a multi-chamber cylinder is installed on a hydraulic integrated block, and a plurality of composite cavities evenly distributed with the power output shaft as the center are provided on the multi-chamber cylinder, and a composite piston rod is installed in each composite cavity to form three multi-chamber hydraulic cylinders, and an inner cylinder is coaxially fixed in the composite cavity, and an inner piston cavity is provided in the inner cylinder, and a gap is provided between the outer wall of the inner cylinder and the inner wall of the composite cavity to form an outer piston cavity, and the composite piston rod includes an outer piston rod matching with the outer piston cavity and an inner piston rod matching with the inner piston cavity, and the inner piston rod is coaxially fixed on the outer piston rod, and a sliding cavity matching with the inner cylinder is formed between the inner piston rod and the outer piston rod, and the inner The piston rod is installed in the inner piston cavity, and the outer piston rod is installed in the outer piston cavity, so that the inner cylinder is slidably assembled in the sliding cavity, the rodless cavity formed by the inner piston rod in the inner piston cavity is the first effective cavity, the rodless cavity formed by the outer piston rod in the outer piston cavity is the second effective cavity, and the rod cavity formed by the outer piston rod in the outer piston cavity is the third effective cavity. The first effective cavity, the second effective cavity, and the third effective cavity are respectively connected to the external two-position three-way control valve through separate oil circuits on the hydraulic integrated block, the high-pressure oil circuit of the two-position three-way control valve is connected to the oil outlet of the proportional throttle valve, and the low-pressure oil circuit of the two-position three-way control valve is connected to the oil tank of the constant pressure variable oil source.

[0010] In the above embodiment, the rotating swash plate mechanism includes a ball bearing seat, a limiting pressure plate, a swash plate, a power output shaft and a ball bearing seat baffle, the swash plate is fixed on the power output shaft, the ball bearing seat baffle and the limiting pressure plate are coaxially sleeved on the power output shaft, the limiting pressure plate is fixed on the side of the swash plate facing the multi-chamber hydraulic cylinder by screws, the outer diameter of the limiting pressure plate is larger than the inner diameter of the ball bearing seat baffle, the ball bearing seat baffle is axially limited between the limiting pressure plate and the swash plate by the limiting pressure plate, the ball bearing seat baffle is slidably connected with the limiting pressure plate, a gap is provided between the ball bearing seat baffle and the swash plate to form a sliding area for the ball bearing seat to slide, a limiting hole is provided on the ball bearing seat baffle at a position corresponding to each ball bearing seat, one end of the ball bearing seat is smaller than the diameter of the limiting hole as the limiting end, and the other end is larger than the diameter of the limiting hole as the sliding end, the limiting end of the ball bearing seat is arranged in the limiting hole, and the sliding end of the ball bearing seat is arranged in the sliding area and is slidably connected with the swash plate.

[0011] In the above embodiment, three multi-chamber hydraulic cylinders are provided.

[0012] The present invention also includes a control system for controlling the above-mentioned high-efficiency continuous rotating hydraulic joint, including an inner ring control system, the inner ring control system includes a high-efficiency load matching controller; a torque speed sensor for monitoring the rotation angle of the power output shaft and the load torque on the power output shaft is installed on the power output shaft of the rotating swash plate mechanism; the high-efficiency load matching controller is electrically connected to the two-position three-way control valve and the torque speed sensor; the high-efficiency load matching controller obtains the load torque of the power output shaft through the torque speed sensor M L And the rotation angle of the power output shaft θ Value, the specific control method of the high-efficiency load matching controller is as follows: S1. Detect the rotation angle of the power output shaft θ , using the corner θ Real-time calculation of the control quantity of the two-position three-way control valve corresponding to each effective cavity at this time Control combination and corresponding output torque M , all output torque M Sort from small to large to form an array M I , each group M I The corresponding control amount The control array of X I , thus forming a data set [ M I , X I ];in, I Indicates that the order of data groups is 1, 2, 3..., The control amount of the two-position three-way control valve corresponding to each effective cavity; The value is 0 or 1. =0, indicating the effective area of ​​the effective cavity The corresponding cavity is connected to the low-pressure oil circuit. =1, indicating the effective area The corresponding cavity is connected to the high-pressure oil circuit, where Indicates multi-chamber hydraulic cylinders, n represents the nth effective chamber in each multi-chamber hydraulic cylinder; S2. Detect the load torque of the power output shaft M L ,Bundle I Each group in the data set M I The value of load torque M L Compare one by one and calculate M I - M L , for the obtained To compare, take Greater than 0 and The value is the minimum M I , and record this time M I Corresponding I The value is the initial value I 初 ; S3. Confirm I The final value of the value I 终 , select the first I 终 Group X I As the final control quantity, the two-position three-way control valve is controlled: Assume that the expected tracking accuracy is δ , the angle error is The error change trend is The expected turning angle is θ exp , where Δ θ = θ exp -θ ;

[0013] set up , for I The adjustment range is , , It is a human input value; set up I 终 for I The final determined value of value; where: When| |≦ δ hour: I 终 = I 初 ; When| |> δ and hour: hour, I 终 = I 初 - ; hour, I 终 = I 初 - ; When| |> δ and hour: hour, I 终 = I 初 + ; hour, I 终 = I 初 + .

[0014] In the above implementation, in step S3, =3, =1.

[0015] In the above embodiment, in step S1, the control amount of the two-position three-way control valve corresponding to the effective cavity in each multi-cavity hydraulic cylinder is calculated. And the corresponding output torque M The specific method is as follows: There are three multi-chamber hydraulic cylinders, and the nine effective working chambers of the three groups of multi-chamber hydraulic cylinders are respectively set as the first effective chamber, the second effective chamber, the third effective chamber, the fourth effective chamber, the fifth effective chamber, the sixth effective chamber, the seventh effective chamber, the eighth effective chamber, and the ninth effective chamber; Let the intersection center of the swash plate and the power output shaft axis be point O; Assume the axis of the power output shaft is the y-axis and establish a rectangular coordinate system oxyz ; Assume that the distance between the composite piston rod axis and the power output shaft axis is R ; Assume that when the composite piston rod is retracted to the limit, draw a vertical line from the ball bearing center at the end of the composite piston rod to the axis of the power output shaft, i.e., the y-axis. The intersection of the vertical line and the y-axis is O1. The intersection of the vertical line and the central axis of the swash plate is O2. The distance from O1 to O2 is the motion radius r of the power output shaft. Assuming that when the swash plate rotates, the composite piston rod of the multi-chamber hydraulic cylinder extends to the limit state and contracts to the limit state, the movement stroke of the composite piston rod is H ; Assume the rotation angle of the power output shaft is θ ; Assume that the ball bearing centers of the three composite piston rods are in the rectangular coordinate system oxyz The positions in y 1. y 2, y 3, then:

[0016] Assume the output torque of the power output shaft is M The output forces of the three composite piston rods are F 1. F 2. F 3According to the law of conservation of energy, the following formula is established:

[0017] Substituting formula (1) into formula (2), we can derive the following formula:

[0018] Assume that the comprehensive effective area of ​​the first multi-chamber hydraulic cylinder among the three multi-chamber hydraulic cylinders is S 1, where S 1 is formed by the first effective cavity, the second effective cavity and the third effective cavity. The effective area of ​​the first effective cavity is S 11 The control quantity of the two-position three-way control valve connected to it is x 11 , the effective area of ​​the second effective cavity is S 12 The control quantity of the two-position three-way control valve connected to it is x 12 , the effective area of ​​the third effective cavity is S 13 The control quantity of the two-position three-way control valve connected to it is x 13 ; The comprehensive effective area of ​​the second multi-chamber hydraulic cylinder is S 2, where S 2 is formed by the fourth effective cavity, the fifth effective cavity and the sixth effective cavity, and the effective area of ​​the fourth effective cavity is S 21 The control quantity of the two-position three-way control valve connected to it is x 21 , the effective area of ​​the fifth effective cavity is S 22 The control quantity of the two-position three-way control valve connected to it is x 22 , the effective area of ​​the sixth effective cavity is S23 The control quantity of the two-position three-way control valve connected to it is x 23 ; The comprehensive effective area of ​​the third multi-chamber hydraulic cylinder is S 3, among which S 3 is formed by the seventh effective cavity, the eighth effective cavity and the ninth effective cavity, and the effective area of ​​the seventh effective cavity is S 31 The control quantity of the two-position three-way control valve connected to it is x 31 , the effective area of ​​the eighth effective cavity is S 32 The control quantity of the two-position three-way control valve connected to it is x 32 , the effective area of ​​the ninth effective cavity is S 33 The control quantity of the two-position three-way control valve connected to it is x 33 ; but:

[0019] Among them, the control quantity of the two-position three-way control valve The value is 0 or 1. =0, indicating the effective area The corresponding cavity is connected to the low-pressure oil circuit. =1, indicating the effective area The corresponding cavity is connected to the high-pressure oil circuit; Assume that the pressure at the output port of the proportional throttle valve is P , then according to formula (3) we can get:

[0020] Effective area of ​​multi-chamber hydraulic cylinder S k The relationship between the effective cavity area and the effective cavity area is as follows:

[0021] Substituting equation (6) into equation (5), we get M The expression is as follows:

[0022] Turn the corner θ Substitute the value of into formula (7) to calculate the control quantity of all two-position three-way control valves x 11 , x 12 ,x 13 , x 21 , x 22 , x 23 , x 31 , x 32 , x 33 Control combination and corresponding output torque M .

[0023] In the above embodiment, an outer loop control system is also included, and the outer loop control system is synchronously controlled with the inner loop control system. The outer loop control system includes a high-precision servo tracking controller and a proportional throttle valve. θ The feedback is input into the high-precision servo tracking controller, which calculates the control amount of the proportional throttle valve through the PID control algorithm, adaptive control algorithm or predictive control algorithm. u , by controlling the amount u Fine-tune the proportional throttle valve core opening.

[0024] By adopting the above scheme, the present invention has the following beneficial effects: (1) The composite piston rod of the multi-chamber hydraulic cylinder of the present invention performs telescopic movement, which pushes the end of the composite piston rod to perform reciprocating movement along the axis direction of the composite piston rod. Since the ball bearing is constrained by the swash plate structure, the ball bearing seat can move radially and circumferentially along the swash plate at the end surface of the swash plate, so that when the composite piston rod performs reciprocating movement, it pushes the swash plate to rotate, thereby driving the power output shaft to rotate. The composite piston rod performs a reciprocating stroke movement, and the power output shaft rotates one circle, and finally the linear reciprocating movement of the composite piston rod is converted into a continuous rotational movement of the power output shaft, thereby realizing the continuous rotational movement of the rotary hydraulic joint of the present invention; (2) Since the multi-chamber cylinder barrel and the composite piston rod of the multi-chamber hydraulic cylinder adopt a linear hydraulic cylinder sealing method, the internal leakage is small. Through the control of the two-position three-way control valve, all effective chambers of the multi-chamber hydraulic cylinder are connected to the high-pressure oil circuit, and then the proportional throttle valve is controlled to close, so that the hydraulic locking of the device under high load can be achieved; (3) In the example of the present invention, nine two-position three-way control valves are used to control the oil inlet or oil return of nine effective cavities respectively. A plurality of multi-cavity hydraulic cylinders drive the rotating swash plate mechanism to convert the liquid pressure into the rotation torque of the power output shaft. There are 36 combination modes for the oil inlet or oil return control of the nine effective cavities. At each rotation angle at a moment, 36 torque outputs can be achieved to match the 36 load torques. Since the two-position three-way control valve is a switch valve, the throttling power loss is very small. Therefore, the load matching control method of the rotary hydraulic joint of the present invention is highly efficient. (4) When the rotation angle of the power output shaft is in different angular displacement states, the output torque can be greater than zero or less than zero through different control combinations of the nine two-position three-way control valves, thereby realizing forward and reverse control or continuous rotation control of the power output shaft; (5) The present invention also connects a proportional throttle valve to the common oil inlet high-pressure oil line of the two-position three-way control valve, and the control quantity calculated by the outer loop control system u , the valve core opening of the proportional throttle valve is finely adjusted in real time. Since the throttling amount of the proportional throttle valve is very small, on the one hand, continuous and fine adjustment of the pressure on the high-pressure oil line is achieved, thereby improving the high-precision torque and position control of the present invention. On the other hand, the power loss caused is also small, thereby ensuring high efficiency of the drive; To summarize, the present invention corresponds to the different angular positions of the power output shaft and adopts different load matching control methods. Combined with the fine-tuning of the proportional throttle valve, it can achieve high-precision constant torque control of the rotary hydraulic joint of the present invention under continuous rotational motion state, and can also achieve high-precision variable torque control to match the changing load torque, thereby achieving high-precision force and position servo control. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a structural principle diagram of the high-efficiency continuous rotating hydraulic joint of the present invention.

[0026] Figure 2 It is a schematic diagram of the structure of the high-efficiency continuous rotating hydraulic joint of the present invention, wherein Figure 2 (a) is a front view of the high-efficiency continuous rotation hydraulic joint of the present invention; Figure 2 (b) Figure 2 (a) Cross-sectional view at AA; Figure 2 (c) Figure 2 (a) Cross-sectional view at BB.

[0027] Figure 3 It is a structural schematic diagram of the swash plate mechanism of the present invention, wherein Figure 3 (a) is a perspective view of the output side of the swash plate mechanism of the present invention; Figure 3 (b) is a schematic diagram of the structure of the connection between the swash plate mechanism and the composite piston rod of the present invention; Figure 3 (c) is a schematic diagram of the structure of the connection between the ball bearing seat and the rotating swash plate mechanism of the present invention.

[0028] Figure 4 It is a stereoscopic diagram of the high-efficiency continuous rotating hydraulic joint of the present invention.

[0029] Figure 5 This is a structural principle diagram of the high-efficiency continuous rotating hydraulic joint of the present invention.

[0030] Figure 6This is the control principle diagram of the present invention.

[0031] Figure 7 This is a control principle diagram of the high-efficiency load matching controller of the present invention.

[0032] Figure 8 The rotation angle error of the present invention With speed And error accuracy Schematic diagram of the relationship.

[0033] Fig. 9 This is the hydraulic drive schematic diagram of the existing multi-joint mechanical structure.

[0034] In the attached drawings: 1. two-position three-way control valve; 2. hydraulic integrated block; 3. multi-chamber hydraulic cylinder; 31. multi-chamber cylinder barrel; 311. composite cavity; 312. inner cylinder barrel; 32. composite piston rod; 321. outer piston rod; 322. inner piston rod; 4. rotating swash plate mechanism; 41. ball bearing seat baffle; 42. ball bearing seat; 43. swash plate; 44. power output shaft; 45. limit pressure plate; 5. housing support structure; 6. proportional throttle valve. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0037] like Figure 1 , Figure 2As shown in (b), a high-efficiency continuous rotating hydraulic joint includes a shell support structure 5 and a rotating swash plate mechanism 4, the rotating swash plate mechanism 4 includes a swash plate 43 and a power output shaft 44, the swash plate 43 is driven by three groups of multi-chamber hydraulic cylinders 3 to realize the positive and negative rotation of the power output shaft 44, the three groups of multi-chamber hydraulic cylinders 3 are evenly arranged below the swash plate 43 with the power output shaft 44 as the center, the composite piston rod 32 of the multi-chamber hydraulic cylinder 3 is arranged parallel to the power output shaft 44, the lifting end of the composite piston rod 32 is connected to the ball bearing seat 42 through a ball bearing, and the lifting end of the composite piston rod 32 is slidably assembled on the swash plate 43 through the ball bearing seat 42, the multi-chamber hydraulic cylinder 3 and the rotating swash plate mechanism 4 are both sealed in the shell support structure 5, and only the output end of the power output shaft 44 protrudes from the shell support structure 5.

[0038] Specifically: Figure 2 (b) Figure 2 As shown in (c), the multi-chamber hydraulic cylinder 3 includes a multi-chamber cylinder barrel 31, which is installed on the hydraulic integrated block 2. The multi-chamber cylinder barrel 31 is provided with three composite cavities 311 evenly arranged with the power output shaft 44 as the center. A composite piston rod 32 is installed in each composite cavity 311 to form three groups of multi-chamber hydraulic cylinders 3. The composite cavity 311 is coaxially threadedly connected with an inner cylinder barrel 312, and an inner piston cavity is provided in the inner cylinder barrel 312. A gap is provided between the outer wall of the inner cylinder barrel 312 and the inner wall of the composite cavity 311 to form an outer piston cavity. The composite piston rod 32 includes an outer piston rod 321 that cooperates with the outer piston cavity and an inner piston rod 322 that cooperates with the inner piston cavity. The inner piston rod 322 is coaxially threadedly connected to the outer piston rod 321, and the inner piston rod 322 is connected to the outer piston rod A sliding cavity matching the inner cylinder 312 is formed between 321, the inner piston rod 322 is installed in the inner piston cavity, and the outer piston rod 321 is installed in the outer piston cavity, so that the inner cylinder 312 is slidably assembled in the sliding cavity, the rodless cavity formed by the inner piston rod 322 in the inner piston cavity is the first effective cavity, the rodless cavity formed by the outer piston rod 321 in the outer piston cavity is the second effective cavity, and the rod cavity formed by the outer piston rod 321 in the outer piston cavity is the third effective cavity, the first effective cavity, the second effective cavity, and the third effective cavity are respectively connected to the external two-position three-way control valve 1 through separate oil circuits on the hydraulic integrated block 2, the high-pressure oil circuit of the two-position three-way control valve 1 is connected to the oil outlet of the proportional throttle valve 6, and the low-pressure oil circuit of the two-position three-way control valve is connected to the oil tank of the constant pressure variable oil source; like Figure 3 (a) Figure 3 (b) Figure 3 As shown in (c), the swash plate mechanism 4 includes a ball bearing seat 42, a limit pressure plate 45, a swash plate 43, a power output shaft 44 and a ball bearing seat baffle 41.

[0039] The swash plate 43 is welded to the power output shaft 44, the ball bearing seat baffle 41 and the limit pressure plate 45 are coaxially sleeved on the power output shaft 44, the limit pressure plate 45 is fixed on the side of the swash plate 43 facing the multi-chamber hydraulic cylinder 3 by screws, the outer diameter of the limit pressure plate 45 is larger than the inner diameter of the ball bearing seat baffle 41, the ball bearing seat baffle 41 is axially limited between the limit pressure plate 45 and the swash plate 43 by the limit pressure plate 45, and there is a sliding space between the ball bearing seat baffle 41 and the limit pressure plate 45. A gap is provided between the ball bearing seat baffle 41 and the swash plate 43 to form a sliding area for the ball bearing seat 42 to slide. A limiting hole is provided on the ball bearing seat baffle 41 at a position corresponding to each ball bearing seat 42. One end of the ball bearing seat 42 is smaller than the diameter of the limiting hole as the limiting end, and the other end is larger than the diameter of the limiting hole as the sliding end. The limiting end of the ball bearing seat 42 is arranged in the limiting hole, and the sliding end of the ball bearing seat 42 is arranged in the sliding area and is slidably connected to the swash plate 43.

[0040] The ball bearing seat baffle 41 moves along with the multi-chamber hydraulic cylinder 3 , and the limit pressing plate 45 rotates in conjunction with the swash plate 43 .

[0041] like Figure 2 (a) Figure 2 As shown in (b), the three composite piston rods 32 symmetrically distributed along the center will move in a direction parallel to the axis of the power output shaft 44, and the composite piston rods 32 will push the ball bearing seat 42 to move in a direction parallel to the axis of the power output shaft 44. Due to the constraint of the ball bearing seat baffle 41 and the swash plate 43 in a direction parallel to the axis of the power output shaft 44, the ball bearing seat 42 cannot move in a direction parallel to the axis of the power output shaft 44 when the swash plate 43 does not rotate. On the contrary, the movement of the ball bearing seat 42 in a direction parallel to the axis of the power output shaft 44 will push the swash plate 43 to rotate.

[0042] According to the above structure, the present invention provides a method for continuous rotation control of a rotary hydraulic joint: like Figure 1 As shown, each multi-chamber hydraulic cylinder 3 in the high-efficiency continuous rotating hydraulic joint of the present invention has three effective working chambers. The three multi-chamber hydraulic cylinders 3 of the present invention have a total of nine effective working chambers, which are respectively set as the first effective chamber, the second effective chamber, the third effective chamber, the fourth effective chamber, the fifth effective chamber, the sixth effective chamber, the seventh effective chamber, the eighth effective chamber, and the ninth effective chamber.

[0043] The above nine effective action chambers are respectively connected to a two-position three-way control valve through an oil circuit, and the two-position three-way control valve is connected to the high-pressure oil circuit P or the low-pressure oil circuit T; like Figure 5 As shown, the intersection center of the swash plate 43 and the axis of the power output shaft 44 is point O; Assume that the axis of the power output shaft 44 is the y-axis and the radial direction of the power output shaft 44 is the z-axis. Figure 5 The rectangular coordinate system shown oxyz .

[0044] Assume that the distance between the axis of the composite piston rod 32 and the axis of the power output shaft 44 is R .

[0045] like Figure 5 As shown, when the composite piston rod is retracted to the limit, a vertical line is drawn from the center of the ball bearing at the end of the composite piston rod to the axis of the power output shaft, i.e., the y-axis. The intersection of the vertical line and the y-axis is O1. The vertical line continues to extend and intersects with the central axis of the swash plate at O2. The distance from O1 to O2 is the motion radius r of the power output shaft. Assume that when the swash plate rotates, the distance between the composite piston rod 32 of the same multi-chamber hydraulic cylinder 3 extending to the limit state and contracting to the limit state is the movement stroke of the composite piston rod 32 H .

[0046] Assume that the rotation angle of the power output shaft 44 is θ .

[0047] Assume that the ball bearing centers of the three composite piston rods 32 are in the rectangular coordinate system oxyz The positions in y 1. y 2, y 3. According to the triangle similarity theorem, there is the following corresponding relationship:

[0048] Assume that the output torque of the power output shaft 44 is M The output forces of the three composite piston rods 32 are F 1. F 2. F 3According to the law of conservation of energy, there is the following formula:

[0049] Substituting formula (1) into formula (2), we can derive the following formula:

[0050] Assume that the comprehensive effective area of ​​the first multi-chamber hydraulic cylinder among the three multi-chamber hydraulic cylinders is S 1, where S 1 is formed by the first effective cavity, the second effective cavity and the third effective cavity. The effective area of ​​the first effective cavity is S 11 The control quantity of the two-position three-way control valve connected to it isx 11 , the effective area of ​​the second effective cavity is S 12 The control quantity of the two-position three-way control valve connected to it is x 12 , the effective area of ​​the third effective cavity is S 13 The control quantity of the two-position three-way control valve connected to it is x 13 ; The comprehensive effective area of ​​the second multi-chamber hydraulic cylinder is S 2, where S 2 is formed by the fourth effective cavity, the fifth effective cavity and the sixth effective cavity, and the effective area of ​​the fourth effective cavity is S 21 The control quantity of the two-position three-way control valve connected to it is x 21 , the effective area of ​​the fifth effective cavity is S 22 The control quantity of the two-position three-way control valve connected to it is x 22 , the effective area of ​​the sixth effective cavity is S 23 The control quantity of the two-position three-way control valve connected to it is x 23 ; The comprehensive effective area of ​​the third multi-chamber hydraulic cylinder is S 3, among which S 3 is formed by the seventh effective cavity, the eighth effective cavity and the ninth effective cavity, and the effective area of ​​the seventh effective cavity is S 31 The control quantity of the two-position three-way control valve connected to it is x 31 , the effective area of ​​the eighth effective cavity is S 32 The control quantity of the two-position three-way control valve connected to it is x 32 , the effective area of ​​the ninth effective cavity is S 33 The control quantity of the two-position three-way control valve connected to it is x 33 ; Then there is the following formula:

[0051] The control quantity of the two-position three-way control valve The value is 0 or 1. =0, indicating the effective area The corresponding cavity is connected to the low-pressure oil circuit. =1, indicating the effective area The corresponding cavity is connected to the high-pressure oil circuit.

[0052] By controlling The value of effective area Can appear 2 3 = 8 different values.

[0053] Assume that the pressure at the output port of proportional throttle valve 6 is P , formula (3) can be expressed as follows:

[0054] During the design, if the effective action chambers of the three composite piston rods of the multi-chamber hydraulic cylinder 3 are designed to be the same, the effective action area S 1. S 2. S 3 are all in 0~ S Changes between S express S k The maximum effective area of ​​​​(k=1, 2, 3).

[0055] As the rotation angle of the power output shaft 44 θ changes through control S k , which can allow M In a very small range of fluctuations, the throttle fine-tuning of the proportional throttle valve 6 is used to fine-tune the P The value of M The constant torque output of the rotary hydraulic joint can achieve continuous rotational motion.

[0056] A control method for constant torque output is given below: As shown in Table 1, the effective action area of ​​the three composite piston rods of the multi-chamber hydraulic cylinder 3 S k Only two states, minimum value 0 and maximum value S, are taken, and the control method shown in Table 1 is used. M The values ​​are taken from Gradually increase to , and then by Gradually reduce to , that is, the torque of the power output shaft 44 M exist and Fluctuations between MThe value of is always greater than zero, that is, the power output shaft will continuously rotate in one direction. Similarly, by adjusting the switch control combination strategy of the nine two-position three-way control valves shown in Table 1, the output angle of the power output shaft can be adjusted to 0. o < θ ≤360 o When the power output shaft outputs torque M The value of is always less than zero, that is, the power output shaft will continuously rotate in the other direction. When the power output shaft is in any rotation angle state, by adjusting the switch control combination strategy of the nine two-position three-way control valves, the power output shaft can output torque M is greater than zero or less than zero, thereby controlling the forward or reverse rotation of the power output shaft; Constant torque high efficiency and high precision control method can control the amount by controlling the two-position three-way control valve , making the composite piston rod S k The value of is not fixed at the maximum value S ,according to M Change up or down S k , further narrowing M range of fluctuation.

[0057]

[0058] in, S k A control and adjustment strategy for taking the value, the effective action area of ​​the multi-chamber hydraulic cylinder 3 S k The relationship between the effective cavity area and the effective cavity area is as follows:

[0059] Substituting equation (6) into equation (5), we can get M The expression is as follows:

[0060] The control quantity of the two-position three-way control valve connected to each effective chamber x k1、 x k2、 x k2 The value of is 1 or 0. M The column corresponds to the output torque formula at different rotation angles of the power output shaft. S k The maximum value of S Replace with S kThe value of In the structural design, the three multi-chamber hydraulic cylinders have the same structure. S k1 =0.9S, S k2 =0.1S, S k3 =0.05S; the three multi-chamber hydraulic cylinders use the same control method at each corner, that is, the comprehensive effective action area of ​​the three multi-chamber hydraulic cylinders S k Similarly, according to the control method shown in Table 2, when the output angle of the power output shaft is 0 o < θ ≤360 o When the power output shaft outputs torque M The value of is always to The range of variation is , adjust the pressure appropriately by adjusting the opening of the proportional throttle valve 6 P , using a smaller throttling pressure drop, that is, a smaller throttling power loss, can M Stable , It is the maximum pressure at the oil outlet of the proportional throttle valve 6.

[0061]

[0062] The variable torque load matching high efficiency control mode of the rotary hydraulic joint of the present invention is as follows.

[0063] From formula (7), we can know that when the structural design is determined, the output angle of the power output shaft is θ When the control quantity of nine two-position three-way control valves is x 11 , x 12 , x 13 , x 21 , x 22 , x 23 , x 31 , x 32 , x 33 Determines the output torque of the hydraulic joint M The control quantity of the two-position three-way control valve has only two state values ​​0 or 1. x 11 , x12 , x 13 , x 21 , x 22 , x 23 , x 31 , x 32 , x 33 Combination, corresponding to different output torque M .

[0064] According to the principle of permutation and combination, the control quantity x 11 , x 12 , x 13 , x 21 , x 22 , x 23 , x 31 , x 32 , x 33 Total Combination, the output angular displacement of each power output shaft θ There are 36 corresponding output torques, and these 36 output torques are recorded as M I ( I =1~36), corresponding x 11 , x 12 , x 13 , x 21 , x 22 , x 23 , x 31 , x 32 , x 33 The control combination is recorded as X I ( I =1~36).

[0065] Real-time monitoring of joint load torque through sensors M L and the rotation angle of the power output shaft θ , the joint load moment M L and corners θ Feedback to the high-efficiency load matching controller, the high-efficiency load matching controller combines the control of the two-position three-way control valve X I Feedback to each two-position three-way control valve; Simultaneously measure the turning angle θ , real-time comparison of expected turning angle θ exp Measured turning angle θ , and obtain the tracking error Δ θ , specifically: Δ θ = θ exp -θ , put Δ θ The feedback quantity is input into the high-precision servo tracking controller. As the outer loop control, the high-precision servo tracking controller calculates the control quantity of the proportional throttle valve through the PID control algorithm, adaptive control algorithm or predictive control algorithm. u , by controlling the amount u The proportional throttle valve core opening is fine-tuned, thereby further achieving the output pressure of the proportional throttle valve through the effect of throttling pressure drop. P Fine-tuning to compensate for the output torque caused by the high-efficiency load matching controller controlling the two-position three-way control valve M Discretization of the output torque M Continuous adjustment of the output torque M and load moment M L For better matching, high-precision tracking control can be achieved.

[0066] Since the throttling loss of the two-position three-way control valve is small, and the throttling control of the proportional throttle valve 6 is only for the pressure P Fine adjustment is performed, that is, the pressure loss caused by the throttling of the proportional throttle valve 6 Small, the power loss caused by throttling of the proportional throttle valve 6 It is also very small, and ultimately the throttling loss of the entire hydraulic circuit is small, achieving high-efficiency drive.

[0067] The control method of the high-efficiency load matching controller is as follows: Specifically: S1. Turn the corner θ Substitute the value of into formula (7) and calculate the angle θ The control volume of all two-position three-way control valves x 11 , x 12 ,x 13 , x 21 , x 22 , x 23 , x 31 , x 32 , x 33 Control combination and corresponding output torque M , all output torque M Sort from small to large to form an array M I ( I =1~36), each group M I The corresponding control amount x 11 , x 12 , x 13 , x 21 , x 22 , x 23 , x 31 , x 32 , x 33 The control combination is recorded as X I ( I =1~36), thus forming the data set [ M I , X I ]; S2. Detect the load torque of the power output shaft M L， Bundle I Each group in the data set M I The value of load torque M L Compare one by one and calculate M I - M L , for the obtained To compare, take Greater than 0 and The smallest value M I , and record this timeM I Corresponding I The value is the initial value I 初 ; S3. Confirm I The final value of the value I 终 , select the first I 终 Group X I As the final control quantity, the two-position three-way control valve is controlled: Assume that the expected tracking accuracy is δ , the angle error is , The desired turning angle θ exp Measured turning angle θ The error trend is set up , for I The adjustment range is And it is a manually input value; The error change trend is Refers to the tendency of the power output shaft 44 to rotate when It is becoming larger, indicating that the error of the power output shaft angle It is gradually getting bigger. ;when It shows a decreasing trend, indicating that the error of the power output shaft angle is gradually decreasing. ; As when| |> δ and When As soon as possible, the trend from increasing to decreasing should be changed. M Increase, need to be in the data group M I Adjust the value in the When It shows a decreasing trend, that is When Originally δ The interval converges. At this time, although the output torque still needs to be M Increase, improve the original However, in order to prevent the convergence speed from being too fast, of The value must be less than of The value of Figure 7 As shown, .

[0068] Therefore, suppose I 终 for I The final value of the value is selected in the data group. I 终 Group X I As the final control quantity, the two-position three-way control valve is controlled; wherein: When| |≦ δ hour: I 终 = I 初 ; When| |> δ and hour: hour, I 终 = I 初 - ; hour, I 终 = I 初 - ; When| |> δ and hour: hour, I 终 = I 初 + ; hour, I 终 = I 初 + .

[0069] Through the above steps, the control accuracy can be further improved.

[0070] By adopting different load matching control methods through the above-mentioned control system and combining the fine-tuning of the proportional throttle valve, high-precision constant torque control of the rotary hydraulic joint of the present invention under continuous rotational motion state can be achieved, and high-precision variable torque control can be achieved to match the changing load torque, thereby achieving high-precision force and position servo control.

Claims

1. A high-efficiency continuous rotation hydraulic joint, comprising a swash plate mechanism (4) for driving the joint to rotate, characterized in that: The rotating swash plate mechanism (4) comprises a swash plate (43) and a power output shaft (44). The swash plate (43) is driven by a plurality of multi-chamber hydraulic cylinders (3) to realize positive and negative rotation of the power output shaft (44). The plurality of multi-chamber hydraulic cylinders (3) are evenly arranged below the swash plate (43) with the power output shaft (44) as the center. The composite piston rod (32) of the multi-chamber hydraulic cylinder (3) is arranged in parallel with the power output shaft (44). The lifting end of the composite piston rod (32) is connected to the ball bearing seat (42) through a ball bearing, and the lifting end of the composite piston rod (32) is slidably assembled on the swash plate (43) through the ball bearing seat (42).

2. The high-efficiency continuous rotation hydraulic joint according to claim 1 is characterized in that: A multi-chamber cylinder barrel (31) is mounted on a hydraulic integrated block (2). The multi-chamber cylinder barrel (31) is provided with a plurality of composite cavities (311) uniformly arranged around a power output shaft (44) as the center. A composite piston rod (32) is mounted in each composite cavity (311) to form three multi-chamber hydraulic cylinders (3). An inner cylinder barrel (312) is coaxially fixed in the composite cavity (311). An inner piston cavity is arranged in the inner cylinder barrel (312). A gap is arranged between the outer wall of the inner cylinder barrel (312) and the inner wall of the composite cavity (311) to form an outer piston cavity. The composite piston rod (32) includes an outer piston rod (321) and an inner piston rod (322). The inner piston rod (322) is coaxially fixed on the outer piston rod (321) and linked thereto. The inner piston rod (322) is linked to the outer piston rod (321). A spacing is provided between the outer piston rods (321) to form a sliding cavity matching the inner cylinder (312); the inner piston rod (322) is installed in the inner piston cavity, the outer piston rod (321) is installed in the outer piston cavity, the inner cylinder (312) is slidably assembled in the sliding cavity, the rodless cavity of the inner piston cavity is the first effective cavity, the rodless cavity in the outer piston cavity is the second effective cavity, and the rod cavity of the outer piston cavity is the third effective cavity. The first effective cavity, the second effective cavity, and the third effective cavity are respectively connected to the external two-position three-way control valve (1) through separate oil circuits on the hydraulic integrated block (2); the high-pressure oil circuit of the two-position three-way control valve (1) is connected to the oil outlet of the proportional throttle valve (6), and the low-pressure oil circuit of the two-position three-way control valve (1) is connected to the oil tank of the constant pressure variable oil source.

3. The high-efficiency continuous rotation hydraulic joint according to claim 2 is characterized in that: The rotating swash plate mechanism (4) comprises a ball bearing seat (42), a limiting pressure plate (45), a swash plate (43), a power output shaft (44) and a ball bearing seat baffle (41); the swash plate (43) is fixed on the power output shaft (44); the ball bearing seat baffle (41) and the limiting pressure plate (45) are both coaxially sleeved on the power output shaft (44); the limiting pressure plate (45) is fixed on the side of the swash plate (43) facing the multi-chamber hydraulic cylinder (3) by screws; the outer diameter of the limiting pressure plate (45) is larger than the inner diameter of the ball bearing seat baffle (41); the ball bearing seat baffle (41) is axially limited on the limiting pressure plate (44) by the limiting pressure plate (45). 5) and the swash plate (43), the ball bearing seat baffle (41) and the limiting pressure plate (45) are slidably connected, a gap is provided between the ball bearing seat baffle (41) and the swash plate (43) to form a sliding area for the ball bearing seat (42) to slide, a limiting hole is provided on the ball bearing seat baffle (41) at a position corresponding to each ball bearing seat (42), one end of the ball bearing seat (42) is smaller than the diameter of the limiting hole as the limiting end, and the other end is larger than the diameter of the limiting hole as the sliding end, the limiting end of the ball bearing seat (42) is arranged in the limiting hole, and the sliding end of the ball bearing seat (42) is arranged in the sliding area and is slidably connected to the swash plate (43).

4. The high-efficiency continuous rotation hydraulic joint according to claim 2 is characterized in that: The multi-chamber hydraulic cylinders (3) are provided in three numbers.

5. A control system for controlling the high-efficiency continuous rotation hydraulic joint according to any one of claims 2 to 4, characterized in that: The invention comprises an inner loop control system, wherein the inner loop control system comprises a high-efficiency load matching controller; a torque speed sensor for monitoring the rotation angle of the power output shaft and the load torque on the power output shaft is installed on the power output shaft of the rotating swash plate mechanism; the high-efficiency load matching controller is electrically connected to the two-position three-way control valve and the torque speed sensor; the high-efficiency load matching controller obtains the load torque M of the power output shaft through the torque speed sensor L As well as the rotation angle θ of the power output shaft, the specific control method of the high-efficiency load matching controller is as follows: S1. Detect the rotation angle θ of the power output shaft, and use the rotation angle θ to calculate in real time the control amount of the two-position three-way control valve corresponding to the effective cavity in each multi-cavity hydraulic cylinder at this moment And the corresponding output torque M, sort all the output torques M from small to large to form an array M I , put the array M I The control quantity corresponding to each output torque M in The resulting array is denoted as X I , thus forming a data set [M I , X I ]; where I indicates that the order of the data groups is 1, 2, 3..., The control amount of the two-position three-way control valve corresponding to each effective cavity; The value is 0 or 1. =0, indicating the effective area of ​​the effective cavity The corresponding cavity is connected to the low-pressure oil circuit. =1, indicating the effective area The corresponding cavity is connected to the high-pressure oil circuit, where Indicates multi-chamber hydraulic cylinders, n represents the nth effective chamber in each multi-chamber hydraulic cylinder; S2, detect the load torque M of the power output shaft L , put the array M in the data group I Each value in is related to the load torque M L Compare one by one and get M I -M L , and then the obtained Compare and select Greater than 0 and The value is the minimum M I , record M at this time I The corresponding I value is the initial value I 初 ; S3. Determine the final value of I 终 , select the data group [M I , X I ] 终 Group X I As the final control quantity, the two-position three-way control valve is controlled. The specific selection method is as follows: Assume that the expected tracking accuracy is δ and the angle error is The error change trend is The expected turning angle is θ exp , where Δ θ = θ exp -θ ; set up , is the number of adjustment steps of I, where , , It is an artificially set value; When| |≦δ: I 终 =I 初 ; When| |>δ and hour: time, I 终 =I 初 - ; time, I 终 =I 初 - ; When| |>δ and hour: time, I 终 =I 初 + ; time, I 终 =I 初 + .

6. The control system of the high-efficiency continuous rotation hydraulic joint according to claim 5 is characterized in that: In step S3, =3, =1.

7. The control system of the high-efficiency continuous rotation hydraulic joint according to claim 5 is characterized in that: In step S1, the control quantity of the two-position three-way control valve corresponding to the effective cavity in each multi-cavity hydraulic cylinder is calculated. And the specific method of the corresponding output torque M is as follows: There are three multi-chamber hydraulic cylinders, and the nine effective working chambers of the three groups of multi-chamber hydraulic cylinders are respectively set as the first effective chamber, the second effective chamber, the third effective chamber, the fourth effective chamber, the fifth effective chamber, the sixth effective chamber, the seventh effective chamber, the eighth effective chamber, and the ninth effective chamber; Let the intersection center of the swash plate and the power output shaft axis be point O; Assume the axis of the power output shaft is the y-axis and establish the rectangular coordinate system oxyz; Assume that the distance between the composite piston rod axis and the power output shaft axis is R; Assume that when the composite piston rod is retracted to the limit, draw a vertical line from the ball bearing center at the end of the composite piston rod to the axis of the power output shaft, i.e., the y-axis. The intersection of the vertical line and the y-axis is O1. The intersection of the vertical line and the central axis of the swash plate is O2. The distance from O1 to O2 is the motion radius r of the power output shaft. Assume that when the swash plate rotates, the composite piston rod of the multi-chamber hydraulic cylinder extends to the limit state and contracts to the limit state, and the movement stroke of the composite piston rod is H; Assume the rotation angle of the power output shaft is θ; Assume that the positions of the ball bearing centers of the three composite piston rods in the rectangular coordinate system oxyz are y1, y2, and y3 respectively, then: ; Assume that the output torque of the power output shaft is M, and the output forces of the three composite piston rods are F1, F2, and F3 respectively. According to the law of conservation of energy, the following formula is established: ; Substituting formula (1) into formula (2), we can derive the following formula: ; Assume that the comprehensive effective action area of ​​the first multi-cavity hydraulic cylinder among the three multi-cavity hydraulic cylinders is S1, where S1 is formed by the first effective cavity, the second effective cavity and the third effective cavity. The effective action area of ​​the first effective cavity is S 11 The control quantity of the two-position three-way control valve connected to it is x 11 , the effective area of ​​the second effective cavity is S 12 The control quantity of the two-position three-way control valve connected to it is x 12 , the effective area of ​​the third effective cavity is S 13 The control quantity of the two-position three-way control valve connected to it is x 13 ; The comprehensive effective action area of ​​the second multi-chamber hydraulic cylinder is S2, where S2 is formed by the fourth effective chamber, the fifth effective chamber and the sixth effective chamber. The effective action area of ​​the fourth effective chamber is S 21 The control quantity of the two-position three-way control valve connected to it is x 21 , the effective area of ​​the fifth effective cavity is S 22 The control quantity of the two-position three-way control valve connected to it is x 22 , the effective area of ​​the sixth effective cavity is S 23 The control quantity of the two-position three-way control valve connected to it is x 23 ; The comprehensive effective action area of ​​the third multi-chamber hydraulic cylinder is S3, where S3 is formed by the seventh effective chamber, the eighth effective chamber and the ninth effective chamber. The effective action area of ​​the seventh effective chamber is S 31 The control quantity of the two-position three-way control valve connected to it is x 31 , the effective area of ​​the eighth effective cavity is S 32 The control quantity of the two-position three-way control valve connected to it is x 32 , the effective area of ​​the ninth effective cavity is S 33 The control quantity of the two-position three-way control valve connected to it is x 33 ; but: ; Among them, the control quantity of the two-position three-way control valve The value is 0 or 1. =0, indicating the effective area The corresponding cavity is connected to the low-pressure oil circuit. =1, indicating the effective area The corresponding cavity is connected to the high-pressure oil circuit; Assuming the pressure at the output port of the proportional throttle valve is P, we can obtain the following equation (3): ; The effective area S of the multi-chamber hydraulic cylinder k The relationship between the effective cavity area and the effective cavity area is as follows: ; Substituting equation (6) into equation (5), we get the expression of M as follows: ; Substitute the value of the rotation angle θ into formula (7) to calculate the control quantity x of all two-position three-way control valves 11 、x 12 、x 13 、x 21 、x 22 、x 23 、x 31 、x 32 、x 33 Control combination and corresponding output torque M.

8. The control system of the high-efficiency continuous rotation hydraulic joint according to claim 5 is characterized in that: The invention also includes an outer loop control system, which includes a high-precision servo tracking controller and a proportional throttle valve. Δθ is input into the high-precision servo tracking controller as a feedback quantity. The high-precision servo tracking controller calculates the control quantity u of the proportional throttle valve through a PID control algorithm, an adaptive control algorithm or a predictive control algorithm, and adjusts the valve core opening of the proportional throttle valve through the control quantity u.

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