A variable gain hydraulic digital valve and large inertia cylinder control method

Abstract

The present invention discloses a variable gain hydraulic digital valve and a large inertia cylinder control method, belonging to the technical field of throttle valves. The hydraulic digital valve of the present invention includes a pilot stage and a main stage; the pilot stage of the present invention includes two two-position three-way proportional ball valves, the upper valve core and the lower valve core in the proportional ball valve valve core assembly are both ball valve cores, and the displacement of the valve core assembly is directly measured by a stepper motor encoder, eliminating the pilot stage displacement sensor. The valve port structure of the main stage of the present invention adopts a non-full-circumference opening form, and the valve port flow segmented control is realized through a U-shaped throttling groove. Through speed planning in different time periods, the present invention not only realizes the rapid movement requirements of the large inertia cylinder, but also realizes the problem of precise displacement control of the large inertia system.

Description

Technical Field

[0001] The invention relates to the technical field of throttle valves, and in particular to a variable gain hydraulic digital valve and a large inertia cylinder control method. Background Art

[0002] Hydraulic transmission technology is widely used in water conservancy projects, food processing, die-casting and other industries because it is safe, environmentally friendly, has high power density and can easily achieve large power output. Among them, water hydraulic valves, as one of the core components in the field of water hydraulic transmission technology, have received widespread attention.

[0003] Digital valves are currently mainly divided into high-speed switching type and incremental digital valves. High-speed switching valves rely on high-frequency opening and closing of electromagnets to achieve discrete flow, and the flow pulsation is large, while incremental digital valves use voice coil motors or stepper motors and rely on pulse control to control the valve core displacement.

[0004] A large inertia hydraulic cylinder refers to a hydraulic cylinder used to drive a mechanism with a large inertia in a hydraulic system (referred to as a large inertia cylinder). It is widely used because it exhibits good stability during movement and has the advantages of little change in movement state when disturbed by external forces. For example: in situations where heavy objects need to be carried and moved, such as in heavy cranes, excavators, loaders and other construction machinery, large inertia hydraulic cylinders can provide the required force and stability; in industrial automation fields such as automated production lines and automated assembly lines, large inertia hydraulic cylinders can be used to drive the positioning of large mechanical arms or heavy components; in construction, such as concrete pump trucks, tower cranes and other equipment, large inertia hydraulic cylinders are used to support and move heavy structures; in oil drilling and mining equipment, large inertia hydraulic cylinders are used to control the precise movement of drill rods and withstand huge underground pressure; in certain aerospace applications, such as the retraction and extension of aircraft landing gear, large inertia hydraulic cylinders can provide the necessary force and stability; in the control mechanisms of dams and sluices, large inertia hydraulic cylinders are used to control the opening and closing of heavy gates; in heavy transport vehicles, such as dump trucks, heavy trucks, etc., large inertia hydraulic cylinders are used to control the lifting and dumping of cargo boxes.

[0005] Large inertia hydraulic cylinders often need to be controlled in sections for high-speed operation and low-speed and high-precision operation. For example, in some applications, such as hot stamping forming pressing processes, large inertia hydraulic cylinders need to respond quickly to meet production efficiency requirements. High-speed operation can reduce throttling losses, improve system efficiency, and provide the necessary power when fast action is required. In situations where precise control is required, such as precision positioning or fine processing, large inertia hydraulic cylinders need to achieve low-speed and high-precision operation. This is because the mechanical time constant of large inertia loads is large, and the response time and overshoot of the system are difficult to reconcile. In addition, in most applications, large inertia hydraulic cylinders have different requirements for control performance in different working stages. At present, digital hydraulic valves are mainly used in the existing technology to control the displacement and speed of large inertia hydraulic cylinders, but the existing digital hydraulic valves and their control strategies are difficult to ensure good control dynamic characteristics. The authorization announcement number is CN114593100B, a plug-in water pressure digital throttle valve with independent load port control and a control method. The patent proposes a structure in which two two-position three-way proportional valves are used to control the upper and lower chambers of the main valve respectively. The pilot stage adopts the structure of a ball valve and a plate valve. Due to the large flow area gain of the plate valve, it is difficult to achieve the optimal state of the main valve displacement control; and because the main stage is a full-circle opening form, the area gain is large and the flow gradient is large, which is difficult for occasions that require precise load control. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and propose a variable gain hydraulic digital valve and a large inertia cylinder control method. The variable gain hydraulic valve includes a pilot valve and a main valve, the electro-mechanical converter is a stepper motor ball screw, the stepper motor is equipped with an encoder, and the valve cores on the left and right sides are of the same structure; the valve cores on both sides of the pilot stage are used to supply liquid to the upper and lower chambers of the main stage, and the main stage valve core displacement closed-loop control is realized in combination with the displacement sensor on the main stage, and different main stage valve core displacements correspond to different flow rates.

[0007] The present invention first provides a variable gain hydraulic digital valve, comprising a pilot valve and a main valve; the pilot valve comprises two two-position three-way proportional ball valves of the same structure, arranged on the same valve block and independently controlled; the main valve is a two-way plug-in cone slide valve structure, and the main valve has an upper control chamber and a lower control chamber respectively connected to the working ports of the two proportional ball valves; the position of the main valve core is adjusted by adjusting the pressure difference between the two control chambers,

[0008] The valve core assembly of the proportional ball valve is driven by a stepper motor ball screw, and an encoder is installed on the stepper motor; the valve core assembly includes a guide rod, an upper valve core, a flow rod, and a lower valve core, wherein the upper valve core and the lower valve core are both ball valve cores, the upper valve core is used for flow control between the pilot valve T port and the working port, and the lower valve core is used for flow control between the pilot valve P port and the working port, the upper end of the guide rod is connected to the ball screw, and the lower end is connected to the upper valve core, the flow rod is located between the upper valve core and the lower valve core, the upper end of the flow rod is provided with a conical surface for matching the upper valve core, and the lower end is in contact with the lower valve core, and the flow rod is provided with a through hole for connecting the T port and the working port along the axis; a spring reset assembly is provided below the lower valve core; when the upper valve core and the lower valve core are both in the upper limit position, only the T port of the proportional ball valve is connected to the working port;

[0009] The end of the main valve core is evenly distributed with a plurality of U-shaped throttling grooves in the circumferential direction; when the displacement of the valve core is less than the length of the U-shaped throttling groove, the hydraulic digital valve controls the flow of the high water base fluid through the U-shaped throttling groove. In this case, due to the small displacement of the valve core, the flow of the oil through the U-shaped throttling groove is restricted, thereby achieving control of the flow rate. When the displacement of the valve core exceeds the length of the U-shaped throttling groove, the flow state of the hydraulic digital valve will change. At this time, the displacement of the valve core is large, the limiting effect of the U-shaped throttling groove is weakened, the resistance to the flow of the high water base fluid is reduced, and the flow rate increases.

[0010] The present invention realizes segmented and demand-based control of the flow area gradient by adopting the form of a U-shaped non-full-circumference valve port + a full-circumference opening. When high-precision flow is required, a U-shaped throttling groove with a small area gradient is adopted, and when high rapidity is required, a full-mouth opening with a large area gradient is adopted to meet precise control when different needs are met.

[0011] The present invention also provides a large inertia cylinder control method based on the hydraulic digital valve, wherein the hydraulic digital valve controls an external hydraulic cylinder connected thereto to achieve a set displacement, and the control method comprises the following steps:

[0012] 1) According to the set working displacement that the external hydraulic cylinder needs to achieve, the deceleration point position of the external hydraulic cylinder is pre-set; wherein, before the output displacement of the external hydraulic cylinder reaches the deceleration point position, the external hydraulic cylinder runs at a high speed; after reaching the deceleration point position, the external hydraulic cylinder runs at a low speed and high precision until the required set working displacement is achieved;

[0013] 2) When the external hydraulic cylinder just starts to work, the two proportional ball valves of the hydraulic digital valve are controlled to move the main valve core to the set first opening, which is greater than the length of the U-shaped throttling groove. At the first opening, the main valve does not play a throttling role; at this time, the liquid flows into the oil inlet of the main valve and is transported to the external hydraulic cylinder through the oil outlet, and the external hydraulic cylinder acts at high speed to output displacement;

[0014] 3) Keep the displacement of the main valve spool unchanged until the output displacement of the external hydraulic cylinder reaches the deceleration point position set in step 1);

[0015] 4) After reaching the deceleration point, the two proportional ball valves of the hydraulic digital valve are controlled to gradually reduce the displacement of the main valve core to the second opening, wherein the displacement of the main valve core is less than the length of the U-shaped throttling groove at the second opening, and the main valve plays a throttling role at the second opening; at this stage, the speed of the external hydraulic cylinder is reduced, and the hydraulic digital valve can accurately control the speed of the hydraulic cylinder;

[0016] 5) Continue to maintain the main valve spool displacement unchanged until the output displacement of the external hydraulic cylinder reaches the required working displacement.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The two-position three-way proportional ball valve of the present invention eliminates the pilot displacement sensor and directly uses the stepper motor encoder for measurement, thereby achieving precise control. In the two-position three-way proportional ball valve of the present invention, both the upper and lower valve cores use ball valve cores, and the ball valve has an automatic centering function, achieving high-reliability water hydraulic sealing and pilot proportional control; the working medium in the liquid circuit of the pilot valve and the main valve of the present invention can be oil, or water or high water-based liquid (when working underground in coal mines), which reduces the requirements for the working medium and makes it suitable for more application scenarios.

[0019] The main valve core of the present invention adopts a U-shaped non-full-circumference opening (U-shaped throttling groove). According to the set external large-inertia hydraulic cylinder working displacement, the present invention proposes a control method for realizing segmented control of the valve port flow. On the one hand, in the high-speed operation stage, it focuses on the dynamic response and efficiency of the system; reduces throttling losses, improves system efficiency, and provides necessary power when rapid action is required. On the other hand, in situations where precise control is required, the present invention focuses on accuracy and stability, can improve the flow control accuracy when the valve port is small, and ensures precise control of the hydraulic cylinder movement. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural diagram of the hydraulic digital valve of the present invention;

[0021] Figure 2 This is a structural diagram of the present invention when the pilot stage is not in action;

[0022] Figure 3 This is a structural diagram of the present invention when the single-side valve core is in action;

[0023] Figure 4 It is the main structure diagram of the present invention;

[0024] Figure 5 This is a principle diagram of the variable gain main valve of the present invention when it is not in action;

[0025] Figure 6 This is a principle diagram of the variable gain main valve of the present invention when it is in action;

[0026] Figure 7 This is a comparison chart of the flow area of ​​different valve port forms with a diameter of 32;

[0027] Figure 8 It is a valve-controlled cylinder principle diagram of the variable gain hydraulic digital valve of the present invention;

[0028] Fig. 9 A reference motion speed diagram of a hydraulic cylinder in a specific embodiment of the present invention;

[0029] Fig.10 A valve core displacement curve diagram in a specific embodiment of the present invention;

[0030] Fig.11 This is a displacement velocity diagram of the push cylinder in a specific embodiment of the present invention.

[0031] In the figure, 1-stepping motor ball screw; 2-motor seat; 3-valve block; 4-guide rod; 5-guide sleeve; 6-upper valve core; 7-middle sleeve; 8-lower sleeve; 9-flow rod; 10-valve seat; 11-lower valve core; 12-spring seat; 13-spring; 14-limit sleeve; 15-main valve end cover; 16-main valve spring adjusting nut; 17-displacement sensor seat; 18-displacement sensor; 19-displacement sensor push rod; 20-main valve spring; 21-main valve sleeve; 22-main valve core. DETAILED DESCRIPTION

[0032] The present invention is further described and illustrated below in conjunction with specific embodiments. The embodiments are merely exemplary of the present disclosure and do not define the scope of limitation. The technical features of each embodiment of the present invention may be combined accordingly without conflicting with each other.

[0033] like Figures 1 to 5 As shown, the present invention discloses a variable gain hydraulic digital valve, which includes a pilot valve (pilot stage) and a main valve (main stage). The pilot valve includes two two-position three-way proportional ball valves with the same structure, which are arranged on the same valve block 3 and are independently controlled. The main valve is a two-way plug-in cone slide valve structure. The main valve has a liquid inlet and a liquid outlet, and has an upper control chamber and a lower control chamber respectively connected to the working ports of the two proportional ball valves; the position of the main valve core 22 is adjusted by adjusting the pressure difference between the upper control chamber and the lower control chamber, and then the opening between the liquid inlet and the liquid outlet is adjusted.

[0034] In order to achieve precise control of the pilot stage and simplify the pilot stage structure, the pilot stage of the present invention cancels the displacement sensor, and instead selects the pilot stage electro-mechanical converter as a stepper motor ball screw 1. The stepper motor is equipped with an encoder, which can accurately control the output displacement of the ball screw, and then accurately control the working mode of the two two-position three-way proportional ball valves. The two-position three-way proportional ball valves on the left and right sides of the pilot stage have the same structure, but are independently controlled; the valve cores on both sides of the pilot stage are used to supply liquid to the upper and lower control chambers of the main stage, and the main stage valve core displacement closed-loop control is realized in combination with the displacement sensor on the main stage. Different main stage valve core displacements correspond to different flow rates and speeds. The hydraulic digital valve of the present invention is connected to an external hydraulic cylinder to realize the control of the stroke and speed of the external hydraulic cylinder (such as a large inertia cylinder).

[0035] The present invention is particularly suitable for controlling the stroke and speed of large inertia cylinders. Large inertia cylinders have a large inertia, and there will be a lag in the initial movement and the movement stop moment, and there will be an overshoot phenomenon in the stop stage. The hydraulic digital valve of the present invention can be well applied to this control scenario through the structural characteristics of structural variable gain. In the initial stage, the valve port of the present invention is opened to the maximum to meet the rapidity requirements of large inertia cylinders; in the movement stop stage, the segmented control method of the main valve core displacement (high-precision throttling control) is combined to achieve the purpose of accurately controlling the displacement of large inertia cylinders.

[0036] Thanks to the design of the pilot stage valve core assembly, the working medium in the pilot stage and the main stage of the present invention can be oil, water or an oil-water mixture. The following embodiments are introduced by taking the main stage and the pilot stage as an example, the medium is a high water-based liquid (water content accounts for 95-97%, oil content accounts for only 3-5%, water is very economical, and is ten thousand times cheaper than the value of thickened hydraulic oil).

[0037] like Figures 1 to 3 As shown, in a specific embodiment of the present invention, the pilot stage is two two-position three-way proportional ball valves, and the two two-position three-way proportional ball valves have the same structure. The valve core assembly mainly includes a guide rod 4, an upper valve core 6, a flow rod 9, and a lower valve core 11. The upper valve core 6 and the lower valve core 11 are both ball valve cores. The upper valve core 6 is used for flow control between the pilot valve T port and the working port, and the lower valve core 11 is used for flow control between the pilot valve P port and the working port. Specifically, in an optional embodiment, the valve core assembly includes a stepper motor ball screw 1, a motor seat 2, a guide rod 4, a guide sleeve 5, an upper valve core 6, an intermediate sleeve 7, a lower sleeve 8, a flow rod 9, a valve seat 10, a lower valve core 11, a spring seat 12, a spring 13, and a limit sleeve 14.

[0038] The stepper motor ball screw 1 is fixed to the motor by screws, and the motor seat 2 is fixed to the valve block 3 by screws; the rotational motion of the stepper motor is converted into the linear motion of the valve core by the ball screw. The upper valve core 6 and the guide rod 4 are connected together by interference fit, so when the stepper motor ball screw 1 pushes the guide rod 4 to move, the upper valve core 6 and the guide rod 4 can be regarded as one body.

[0039] The flow rod 9 has a through hole in the middle and a conical surface at the upper end. Different flow areas are formed by the different spacings between the upper valve core 6 and the guide rod 4, thereby controlling the flow out of the valve body and realizing proportional control of the flow. The inner and outer sides of the intermediate sleeve 7 are designed with sealing ring grooves, on which sealing rings are installed; the flow rod 9 can slide up and down the intermediate sleeve 7 under the push of the guide rod 4; the lower end of the flow rod 9 contacts the lower valve core 11, and as the flow rod 9 continues to move, the lower valve core 11 is pushed to overcome the elastic force of the spring 13 to open the valve core. The lower valve core 11 and the valve seat 10 have different spacings, forming different flow areas, and different flow areas correspond to different flow rates.

[0040] Interconnected radial through holes are provided at the middle sleeve 7 of the two valve core assemblies and extend out of the valve block to form a T port; radial through holes are provided between the lower sleeve 8 and the valve seat 10 of the two valve core assemblies as their respective working ports (i.e., load ports); a limit sleeve 14 is provided below the spring seat 12, and a spring 13 is provided inside the limit sleeve 14 to provide thrust for the spring seat 12; the spring seat 12 pushes the lower valve core 11 against the valve seat 10 through the thrust provided by the spring 13, and interconnected radial through holes are provided at the spring seat 12 of the two valve core assemblies to form a P port for liquid inlet. When the upper valve core and the lower valve core are both at the upper limit position, the lower valve core is tightly pressed against the valve seat under the action of the spring, and at this time, the high water base liquid of the pump station cannot flow to the load port through the lower valve core, while the high water base liquid of the load port can return to the liquid tank through the upper valve core.

[0041] The main valve adopts a two-way plug-in cone slide valve structure, and uses the cone surface to achieve the sealing of the valve core and the valve seat. There are multiple U-shaped throttling grooves evenly distributed around the end of the main valve core. When the valve core displacement is less than the length of the U-shaped throttling groove, the hydraulic digital valve controls the flow of high-water base fluid through the U-shaped throttling groove. In this case, due to the small displacement of the valve core, the flow of oil through the U-shaped throttling groove is restricted, thereby achieving flow control. When the valve core displacement exceeds the length of the U-shaped throttling groove, the flow state of the hydraulic digital valve will change. At this time, the valve core displacement is large, the limiting effect of the U-shaped throttling groove is weakened, the resistance to the flow of high-water base fluid is reduced, and the flow rate increases. By adopting the form of U-shaped non-full-circumference valve port + full-circumference opening, the flow area gradient is controlled in sections and according to different needs. When high-precision flow is required, the small area gradient of the U-shaped throttling groove is used, and when the rapidity requirement is high, the large area gradient of the full-mouth opening is used to meet the precise control when different needs are met.

[0042] like Figure 4 As shown, in a specific embodiment of the present invention, the main valve includes a main valve end cover 15, a through cavity is provided in the main valve end cover 15, a main valve sleeve 21, a main valve core 22, a main valve spring 20 and a displacement sensor are provided in the cavity, a liquid inlet is provided at the end of the main valve sleeve 21 extending out of the cavity, and a liquid return port is provided radially, the main valve core 22 controls the degree of conduction between the liquid inlet and the liquid return port, the main valve spring 20 is used for resetting the main valve core 22, and the main valve displacement sensor 18 is installed on the main valve displacement sensor seat 17 for detecting the displacement of the main valve core; a sealing piston is provided in the middle of the main valve core 22, a lower control chamber is provided on one side of the piston on the main valve sleeve 21, and an upper control chamber is provided on the other side of the piston on the main valve sleeve. A main valve spring adjustment nut 16 is also provided in the main valve cavity, and a displacement sensor push rod 19 is provided at the end of the main valve displacement sensor. The displacement sensor push rod 19 passes through the main valve spring adjustment nut and the main valve spring 20 and contacts the main valve core. The displacement sensor push rod transmits the displacement of the main valve core to the displacement sensor, and then measures the displacement of the main valve core. The displacement sensor push rod is fixedly connected to the main valve core by threads; an axial through hole is provided in the main valve core; the displacement sensor push rod contacts the through hole in the main valve core, and a device is provided at the connection between the displacement sensor push rod and the through hole to guide the liquid flowing into the cavity through the main valve inlet along the through hole in the main valve core to balance the two ends of the main valve core.

[0043] In order to ensure the flow control accuracy when the flow demand is small and the strong flow capacity when the flow demand is large, the present invention selects the form of non-full-circumference opening to achieve the flow control requirements at different stages. The present invention tests the effect of U-type, V-type, K-type and other throttling grooves. Each throttling groove is 3mm long, 2mm wide, and 3mm deep. There are 6 throttling grooves evenly arranged along the circumference of the valve core end. Figure 7 As shown, the flow area of ​​different valve opening forms with 32 diameters is compared. The linearity of the full-circle opening and K-type throttling groove is better than that of the U-type and V-type, but the area gain of the full-circle opening is the largest, the displacement of the valve core is small, the control requirements for the pilot valve are higher, and the control is difficult. On the other hand, the area gain of the throttling groove with a U-shaped opening is a trend of first large and then small, which meets the working requirements and the displacement of the main valve core is about doubled compared to the full-circle opening, reducing the control requirements. Although the response time of the valve is extended, considering that the digital valve does not pursue high-frequency response, the valve port form of the present invention is designed as a U-shaped throttling groove.

[0044] The length, depth and width of the U-shaped throttling groove will affect the flow area. The present invention further studies the influence of the size of the U-shaped throttling groove on the flow area, and finds that the width has a greater influence on the flow area. In addition, considering that high-water-based liquid media have cavitation during use, in order to make the hydraulic digital valve suitable for high-water-based liquid media, the present invention comprehensively considers the flow capacity and the influence of cavitation factors in the optimization design of the size of the U-shaped throttling groove, and finally obtains the following optimization results through collaborative optimization: the length of the U-shaped throttling groove is preferably 25-30% of the maximum displacement of the valve core, the depth is preferably 9-11% of the diameter of the main valve core, and the width is preferably 6-8% of the diameter of the valve core; the number of U-shaped throttling grooves is preferably 6. In a specific embodiment of the present invention, for a 32-diameter valve port, the displacement of the main valve core is 10mm, the number of U-shaped throttling grooves selected is 6, and the length of the U-shaped throttling groove is 3mm, the width is 2mm, and the depth is 3mm. This design can avoid cavitation of high-water-based liquid and ensure precise control.

[0045] The hydraulic digital valve of the present invention is a digital valve spool displacement closed-loop and a push cylinder speed open-loop control; it realizes closed-loop flow control and open-loop control of the push cylinder speed by directly controlling the spool displacement of the digital valve, and realizes stroke monitoring in conjunction with a cylinder displacement sensor. When a specific working point is reached, the digital valve spool is reduced to a specific value, thereby ultimately realizing the control of the cylinder displacement.

[0046] The main valve core of the present invention adopts a non-full-circle opening structure, and the displacement and flow area are in a nonlinear relationship. In the small displacement stage of the valve core, the flow area changes less with the displacement, the flow rate changes less with the displacement, and the flow control is accurate; as the displacement gradually increases, the flow area changes more with the displacement, the flow rate changes more with the displacement, and the flow capacity is strong. Through the combined design of different valve port flow areas, the flow accuracy at small openings and the flow capacity of large flows are guaranteed.

[0047] The influence of the large inertia cylinder is mainly on the control method. Due to its large inertia, there will be a lag in the initial movement and the stop moment of the movement, and there will be overshoot in the stop phase. The water hydraulic digital valve of the present invention uses the structural characteristics of the variable gain valve to open the valve port to the maximum in the initial stage to meet the rapidity requirements of the large inertia cylinder; in the stop phase of the movement, combined with the segmented control method of the main valve core displacement, the purpose of accurately controlling the displacement of the large inertia cylinder is achieved.

[0048] like Fig. 9 As shown, the large inertia cylinder is selected as the push cylinder. The ideal motion speed of the push cylinder under a certain stroke consists of four strokes: uniform acceleration, uniform speed, uniform deceleration and uniform speed. The integral of the curve on the horizontal axis gives the motion stroke of the push cylinder. The maximum speed v of the push cylinder max =Q / A, Q is the maximum flow provided to the push cylinder, A is the area of ​​the rodless cavity of the push cylinder. yThe slow movement speed of the push cylinder is designed to stop the push cylinder immediately to avoid the problem of large displacement control error of the large inertia push cylinder. The time-main valve displacement diagram of the digital valve can be roughly obtained according to the movement speed diagram of the push cylinder. The function of the deceleration point A is to determine whether the push cylinder has reached the deceleration point A of the push cylinder. If the stroke reaches the deceleration point A, the displacement of the hydraulic digital valve spool will decrease; if the stroke does not reach the deceleration point A, the displacement of the hydraulic digital valve spool will remain unchanged. The function of the end point B is to determine whether the push cylinder has completed the entire stroke. If the stroke reaches the end point B, the hydraulic digital valve spool will be closed immediately. From the above analysis, it can be seen that through speed planning in different time periods, the rapid movement requirements of the hydraulic cylinder are realized, and the precise displacement control problem of the large inertia system is also realized.

[0049] The speed of the push cylinder is linearly related to the flow rate of the digital flow valve. Considering that the flow rate through the valve and the displacement of the digital valve core are nonlinear, a certain simplification is made here, and the displacement of the digital valve core is directly made into a trapezoidal diagram to study the motion characteristics of the push cylinder under different valve core displacement parameters, such as Fig.10 and Fig.11 As shown, there are the valve core displacement step diagram and the displacement speed diagram of the push cylinder respectively.

[0050] like Fig.10 As shown, in order to more clearly express the working process of the above device, this embodiment also provides a large inertia cylinder control method based on the hydraulic digital valve, including the following steps:

[0051] 1) According to the set working displacement that the external hydraulic cylinder needs to reach, the deceleration point position A of the external hydraulic cylinder is pre-set; before the output displacement of the external hydraulic cylinder reaches the deceleration point position, the external hydraulic cylinder maintains high-speed operation, and its hydraulic cylinder operation speed is limited by the pump station flow; after reaching the deceleration point position, the external hydraulic cylinder is in low-speed and high-precision control mode due to the throttling effect of the non-full-circle opening of the hydraulic digital valve.

[0052] 2) When the external hydraulic cylinder just starts to work, the two proportional ball valves of the hydraulic digital valve are controlled to move the main valve core to the set first opening, which is greater than the length of the U-shaped throttling groove. At the first opening, the main valve does not play a throttling role; at this time, the liquid flows in from the main valve oil inlet and is transported to the external hydraulic cylinder through the oil outlet, and the external hydraulic cylinder acts at high speed to output displacement;

[0053] 3) Keep the displacement of the main valve spool unchanged until the output displacement of the external hydraulic cylinder reaches the deceleration point position set in step 1);

[0054] 4) After reaching the deceleration point, the two proportional ball valves of the hydraulic digital valve are controlled to gradually reduce the displacement of the main valve core to the second opening, wherein the displacement of the main valve core is less than the length of the U-shaped throttling groove at the second opening, and the main valve plays a throttling role at the second opening; at this stage, the speed of the external hydraulic cylinder is reduced, and the hydraulic digital valve can accurately control the speed of the hydraulic cylinder;

[0055] 5) Continue to maintain the displacement of the main valve core unchanged until the output displacement of the external hydraulic cylinder reaches the required working displacement, that is, deceleration B is achieved.

[0056] From the above analysis, it can be seen that through speed planning in different time periods, the rapid movement requirements of the large inertia cylinder are met, and the precise displacement control problem of the large inertia system is also achieved.

[0057] like Fig.11 It can be seen that the main valve core can realize displacement tracking according to the reference signal. The main valve core has a delay at the beginning, and then the main valve core can quickly track the reference signal. When the deceleration point A is reached, the displacement of the main valve core begins to decrease to a specific value, and then the displacement of the valve core fluctuates around the specific value. When the deceleration point B is reached, the main valve closes quickly and the push cylinder stops moving. The displacement curve of the push cylinder in the figure is differentiated to obtain the velocity curve of the push cylinder. It is found that the movement trend of the push cylinder is uniform acceleration, uniform speed, uniform deceleration, and uniform speed, which realizes the speed control of the push cylinder.

[0058] like Figure 3 , Figure 5 and Figure 6 As shown, the displacement and valve core speed of the main valve of the hydraulic digital valve are determined by the pressure difference between the upper control chamber and the lower control chamber in the main valve core, and the pressure in the upper control chamber and the lower control chamber are respectively controlled by two proportional ball valves connected thereto; the control method of the proportional ball valve is as follows:

[0059] The ball screw of the proportional ball valve converts the rotational motion of the stepper motor into the linear motion of the guide rod, and the guide rod drives the upper valve core to move together; the upper valve core overcomes the gap with the flow rod, and when the upper valve core moves downward and has not yet contacted the flow rod, Figure 5 As shown, at this time, the high water base liquid in the control chamber corresponding to the working port of the proportional ball valve in the main valve enters the pilot valve through the working port of the corresponding pilot valve, and then returns to the oil tank through the T port of the pilot valve;

[0060] When the upper valve core of the proportional ball valve continues to move downward and contacts the flow rod, the upper valve core blocks the through hole connecting the flow rod to the T port. At this time, the oil return channel from the corresponding control chamber in the main valve to the oil tank is in a closed state.

[0061] When the guide rod of the proportional ball valve drives the upper valve core to continue to move downward, the flow rod contacts the lower valve core. As the displacement of the flow rod increases, the flow rod pushes open the lower valve core, and a gap is created between the lower valve core and the valve seat that allows high-water base liquid to pass through. The liquid flows through the gap between the lower valve core and the valve seat to the corresponding control chamber in the main valve, increasing the pressure in the control chamber. Figure 6 As shown in the figure, the oil inlet of the proportional ball valve corresponding to port A is connected to the upper control chamber of the main valve, and the oil return port of the proportional ball valve corresponding to port B is connected to the lower control chamber of the main valve. At this time, there is a pressure difference between the upper control chamber and the lower control chamber. As the pressure difference increases, when it increases to a level sufficient to overcome all other external forces on the main valve core, the gap between the main valve core and the main valve sleeve is opened. At this time, the displacement sensor measures the displacement information of the main valve core and transmits the information to the external controller.

[0062] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. For ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A variable gain hydraulic digital valve, comprising a pilot valve and a main valve; the pilot valve comprises two two-position three-way proportional ball valves of the same structure, arranged on the same valve block and independently controlled; the main valve is a two-way cartridge cone slide valve structure, and the main valve has an upper control chamber and a lower control chamber respectively connected to the working ports of the two proportional ball valves; the position of the main valve core is adjusted by adjusting the pressure difference between the two control chambers, and is characterized in that: The valve core assembly of the proportional ball valve is driven by a stepper motor ball screw, and an encoder is installed on the stepper motor; the valve core assembly includes a guide rod, an upper valve core, a flow rod, and a lower valve core arranged in sequence from top to bottom, wherein the upper valve core and the lower valve core are both ball valve cores, the upper valve core is used for flow control between the pilot valve T port and the working port, and the lower valve core is used for flow control between the pilot valve P port and the working port, the upper end of the guide rod is connected to the ball screw, and the lower end is connected to the upper valve core, the upper end of the flow rod is provided with a conical surface for matching the upper valve core, and the lower end is in contact with the lower valve core; a spring reset assembly is arranged below the lower valve core; when the upper valve core and the lower valve core are both in the upper limit position, only the T port of the proportional ball valve is connected to the working port; The main valve core end is evenly distributed with a plurality of U-shaped throttling grooves in the circumferential direction; when the displacement of the valve core is less than the length of the U-shaped throttling groove, the hydraulic digital valve controls the flow of the liquid through the U-shaped throttling groove; When the valve core displacement exceeds the length of the U-shaped throttling groove, the liquid flow resistance decreases and the flow rate increases.

2. The hydraulic digital valve according to claim 1, characterized in that: The length of the U-shaped throttling groove is 25-30% of the maximum displacement of the main valve core, the depth is 9-11% of the main valve core diameter, and the width is 6-8% of the main valve core diameter; the number of the U-shaped throttling grooves is 6.

3. The hydraulic digital valve according to claim 1, characterized in that: The valve core assembly also includes a guide sleeve, an intermediate sleeve, a lower sleeve, a valve seat and a spring return assembly which are arranged in sequence from top to bottom; wherein the guide sleeve is used to install the guide rod; a through hole for connecting the T port and the working port is provided along the axis of the flow rod; the flow rod sleeve is arranged on the intermediate sleeve, and radial through holes which are connected to each other are provided at the intermediate sleeve positions of the two groups of valve core assemblies and extend out of the valve block to form the T port; the lower sleeve is arranged below the intermediate sleeve, and the valve seat is arranged below the lower sleeve, and a limiting groove for setting the lower valve core is provided on the lower end surface of the valve seat; radial through holes are provided between the lower sleeves and the valve seats of the two groups of valve core assemblies as their respective working ports; the spring return assembly includes a spring seat, a spring and a limiting sleeve, a limiting sleeve is provided below the spring seat, and a spring which provides thrust for the spring seat is provided in the limiting sleeve; the spring seat pushes the lower valve core onto the valve seat through the thrust provided by the spring, and radial through holes which are connected to each other are provided at the spring seats of the two groups of valve core assemblies to form the P port for liquid inlet.

4. The hydraulic digital valve according to claim 3, characterized in that: The inner side and the outer side of the intermediate sleeve are both designed with sealing ring grooves, and sealing rings are installed in the sealing ring grooves.

5. The hydraulic digital valve according to claim 1, characterized in that: The main valve comprises a main valve end cover, a through cavity is arranged in the main valve end cover, a main valve sleeve, a main valve core, a main valve spring and a displacement sensor are arranged in the cavity, a liquid inlet is arranged at the end of the main valve sleeve extending out of the cavity, a liquid return port is arranged radially, the main valve core controls the degree of conduction between the liquid inlet and the liquid return port, the main valve spring is used for resetting the main valve core, and the displacement sensor is used for detecting the displacement of the main valve core; a sealing piston is arranged in the middle of the main valve core, a lower control chamber is arranged on the main valve sleeve on one side of the piston, and an upper control chamber is arranged on the main valve sleeve on the other side of the piston.

6. The hydraulic digital valve according to claim 5, characterized in that: A main valve spring adjusting nut is also provided in the main valve cavity, and a displacement sensor push rod is provided at the end of the displacement sensor. The displacement sensor push rod passes through the main valve spring adjusting nut and the main valve spring and contacts the main valve core. The displacement sensor push rod transmits the displacement of the main valve core to the displacement sensor, thereby measuring the displacement of the main valve core.

7. The hydraulic digital valve according to claim 6, characterized in that: The displacement sensor push rod is fixedly connected to the main valve core by threads; an axial through hole is provided in the main valve core; the displacement sensor push rod contacts the through hole in the main valve core, and a device is provided at the connection between the displacement sensor push rod and the through hole to guide the liquid flowing into the main valve core through the through hole in the main valve core through the main valve inlet into the cavity to balance the two ends of the main valve core.

8. The variable gain hydraulic digital valve according to claim 7, characterized in that: When the upper valve cores of the two two-position three-way proportional ball valves are at the upper limit position, the lower valve core is pressed tightly against the valve seat due to the pressure of the spring. At this time, the liquid in the upper and lower chambers on both sides of the main valve core flows back to the liquid tank through the T port of the pilot valve. The pressure on both sides of the main valve core is the same, the main valve core is pressed against the main valve sleeve, and the main valve is in a closed state.

9. A large inertia cylinder control method based on the hydraulic digital valve according to claim 1, characterized in that: The hydraulic digital valve is used to control an external hydraulic cylinder connected thereto to achieve a set displacement, and the control method comprises the following steps: 1) According to the set working displacement that the external hydraulic cylinder needs to achieve, the deceleration point position of the external hydraulic cylinder is pre-set; wherein, before the output displacement of the external hydraulic cylinder reaches the deceleration point position, the external hydraulic cylinder runs at a high speed; after reaching the deceleration point position, the external hydraulic cylinder runs at a low speed and high precision until the required set working displacement is achieved; 2) When the external hydraulic cylinder just starts to work, the two proportional ball valves of the hydraulic digital valve are controlled to move the main valve core to the set first opening, which is greater than the length of the U-shaped throttling groove. At the first opening, the main valve does not play a throttling role; at this time, the liquid flows into the oil inlet of the main valve and is transported to the external hydraulic cylinder through the oil outlet, and the external hydraulic cylinder acts at high speed to output displacement; 3) Keep the displacement of the main valve spool unchanged until the output displacement of the external hydraulic cylinder reaches the deceleration point position set in step 1); 4) After reaching the deceleration point, the two proportional ball valves of the hydraulic digital valve are controlled to gradually reduce the displacement of the main valve core to the second opening, wherein the displacement of the main valve core is less than the length of the U-shaped throttling groove at the second opening, and the main valve plays a throttling role at the second opening; at this stage, the speed of the external hydraulic cylinder is reduced, and the hydraulic digital valve can accurately control the speed of the hydraulic cylinder; 5) Continue to maintain the main valve spool displacement unchanged until the output displacement of the external hydraulic cylinder reaches the required working displacement.

10. The control method according to claim 9, characterized in that: The displacement and valve core speed of the main valve of the hydraulic digital valve are determined by the pressure difference between the upper control chamber and the lower control chamber in the main valve core. The pressure in the upper control chamber and the lower control chamber are respectively controlled by two proportional ball valves connected thereto; the control method of the proportional ball valve is as follows: The ball screw of the proportional ball valve converts the rotational motion of the stepper motor into the linear motion of the guide rod, and the guide rod drives the upper valve core to move together; the upper valve core overcomes the gap with the flow rod, and when the upper valve core moves downward and has not yet contacted the flow rod, the liquid in the control chamber corresponding to the working port of the proportional ball valve in the main valve enters the pilot valve through the working port of the corresponding pilot valve, and then returns to the oil tank through the T port of the pilot valve; When the upper valve core of the proportional ball valve continues to move downward and contacts the flow rod, the upper valve core blocks the through hole connecting the flow rod to the T port. At this time, the oil return channel from the corresponding control chamber in the main valve to the oil tank is in a closed state; When the guide rod of the proportional ball valve drives the upper valve core to continue to move downward, the flow rod contacts the lower valve core. As the displacement of the flow rod increases, the flow rod pushes open the lower valve core, and a gap allowing liquid to pass through is generated between the lower valve core and the valve seat. The liquid flows to the corresponding control chamber in the main valve through the gap between the lower valve core and the valve seat, causing the pressure in the control chamber to increase.

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