A three-speed hydraulic cylinder

Abstract

The present invention relates to a three-speed hydraulic cylinder: comprising a cylinder body and a piston, wherein the cylinder body is composed of a guide sleeve, a cylinder barrel and an end cover, the cylinder barrel is provided with a cylindrical cylinder hole, the guide sleeve and the end cover are connected to the two ends of the cylinder barrel along the axial direction of the cylinder hole, so that the cylinder hole is closed to form a liquid cavity, and a second liquid passage and a third liquid passage are provided on the hole walls at both ends of the cylinder hole. The cylinder hole is a through hole with a constant diameter, and a clamping limit ring is provided in the middle of the hole wall of the cylinder hole to simplify the processing of the cylinder hole and reduce the processing cost. At the same time, a combined piston is adopted, and a balancing flow channel is provided between the outer peripheral surface of the piston and the cylinder hole. The hydraulic medium maintains a stable flow between adjacent liquid cavities through the balancing flow channel, thereby controlling the pressure difference on both sides of the piston to reduce the axial force of the piston, avoid the piston hitting the limit ring to cause displacement, reduce the elastic deformation and plastic deformation between the piston and the limit ring, and improve the positioning accuracy of the intermediate gear.

Description

Technical Field

[0001] The invention relates to the field of mechanical manufacturing, and in particular to a three-speed hydraulic cylinder. Background Art

[0002] Hydraulic transmission started later than mechanical transmission, but with the development of time, the popularization of hydraulic technology and the continuous expansion of application fields have promoted the continuous development of hydraulic cylinders. A three-speed hydraulic cylinder can be used for shift cylinders, automated production line cylinders, etc.

[0003] The commonly used three-speed hydraulic cylinder uses a solenoid valve for the gear position, but the gear control accuracy is not high, especially the position of the middle gear is difficult to control accurately, resulting in failure to engage the gear and low reliability. In order to achieve the positioning of the middle gear, a cylinder body with a stepped or dumbbell-shaped inner hole is usually used, and the step in the inner hole is used as a limit device, which makes the inner hole processing difficult and costly. In addition, if the pressure difference on both sides of the piston is large, the axial force on the piston is large, and the piston collides with the limit device to produce elastic deformation and plastic deformation, which also makes the gear positioning inaccurate, resulting in failure to engage the gear and low reliability.

[0004] In order to solve the problem of low reliability of the three-speed hydraulic cylinder, some three-speed hydraulic cylinders are controlled by servo motors, but this will result in a relatively complex structure and a relatively high investment cost.

[0005] After patent search, the following patents are related to this application:

[0006] 1. The Chinese invention patent with application number "201010118513.4", application date "2010.01.22", publication number "CN101749298A", publication date "2010.06.23", name "A three-position power cylinder", and applicant "Shiyan Victor Industrial Co., Ltd.", the three-position power cylinder can be either a hydraulic cylinder or a gas cylinder, and its main scheme is: including a cylinder body, only one piston rod, a large chamber is provided in the cylinder body, a large piston is provided in the large chamber, a chamber of a small piston is provided on the large piston, the small piston is fixed to the piston rod, the large piston pushes the small piston, and drives the piston rod to move to a positioning position; the small piston moves again to drive the piston rod to move to the next positioning position; the reset of the small piston can be achieved by using a spring or by using medium pressure. The invention is composed of an initial position, a first positioning position, and a second positioning position to form a three-position power cylinder. During the movement, the shock-absorbing rubber ring is used for buffering, there is no impact, the positioning is accurate, and the service life is long, which can avoid the defects of the existing three-position cylinder. Only one piston rod is provided, and the coaxiality is good, which is suitable for the mechanism which is accurately positioned at three positions and has high movement frequency, such as the automatic selection and shifting mechanism on the automobile gearbox, etc. However, the cylinder body and piston structure of the patent are complicated, the production cost is high, and the installation is cumbersome.

[0007] 2. The Chinese invention patent with application number "201110387572.6", application date "2011.11.25", publication number "CN102384127A", publication date "2012.03.21", title "A three-position oil cylinder driving device for machine tool shifting", and applicant "Guangzhou Zhujiang Machine Tool Factory Co., Ltd.", is a three-position oil cylinder driving device for machine tool shifting, which includes an oil cylinder, a positioning step is provided in the middle of the oil cylinder, and cylinder covers are respectively fixed at both ends of the oil cylinder, and oil ports are provided on the cylinder cover; a first piston and a second piston are slidably provided in the oil cylinder, a positioning step is provided in the middle of the first piston, and the second piston is slidably sleeved on one end of the first piston; at the same time, the oil action area at the right end of the positioning step in the middle of the first piston is smaller than the sum of the oil action areas at the left ends of the first piston and the second piston, but not larger than the oil action area at the left end of the first piston, so as to realize the positioning of the two pistons in three positions. However, the positioning step in the middle of the oil cylinder of the patent has a complex structure, high production cost and cumbersome installation.

[0008] 3. The utility model patent with application number "201020251276.4", application date "2010.06.29", publication number "CN201714741U", publication date "2011.01.19", name "New three-position power cylinder", and applicant "Shiyan Victor Industrial Co., Ltd.". The new three-position power cylinder can be either a hydraulic cylinder or a pneumatic cylinder, and its main scheme is: it includes a cylinder body, a stepped chamber is provided in the cylinder body, a small piston is provided in the small chamber of the stepped chamber, and the inner end of a piston rod is fixedly connected to the small piston; a large piston is provided in the large chamber of the stepped chamber, the outer circle of the large piston is a stepped journal, and the small journal of the stepped journal cooperates with the small chamber; the plunger is sealed and cooperated with the hollow inner cavity of the large piston, and the cylinder body is provided with medium channels of the large chamber and the small chamber, and the large piston drives the small piston forward. When the large piston moves into place, the plunger continues to drive the small piston forward under the air pressure. The utility model is composed of an initial position, a first positioning position, and a second positioning position to form a three-position power cylinder. During the movement, there is no impact, accurate positioning, and high reliability. It is equipped with only one piston rod, which has good coaxiality and is suitable for mechanisms that are accurately positioned in three positions and have a high movement frequency, such as automatic selection and shifting mechanisms on automobile gearboxes. The patent adopts a stepped chamber and a stepped piston, which has a complex structure, high production cost, and cumbersome installation.

[0009] 4. The utility model patent with application number "201420582106.2", application date "2014.10.09", publication number "CN204099335U", publication date "2015.01.14", name "A mechanical three-position hydraulic cylinder", and applicant "Guangdong Tianheng Hydraulic Machinery Co., Ltd.". The utility model patent discloses a mechanical three-position hydraulic cylinder, including a cylinder head, a cylinder bottom, a cylinder barrel, a piston, a piston rod and a limit sleeve. The cylinder head and the cylinder bottom are respectively arranged at both ends of the cylinder barrel, and the cylinder head and the cylinder bottom are respectively provided with a first oil port and a second oil port. The piston is arranged in the cylinder barrel, and the cylinder barrel is provided with a third oil port. The piston includes a first piston and a second piston. The first piston and the second piston are sleeved on the piston rod, and the third oil port and the limit sleeve are located between the first piston and the second piston. The utility model's mechanical three-position hydraulic cylinder increases the displacement of the piston rod by setting a third oil port, and can achieve different stroke working requirements through mechanical limit points and oil supply methods, greatly saving production costs and maximizing production benefits. However, the force-bearing areas of the pistons in this patent are different, and the hydraulic pressure when the pistons are balanced is difficult to control.

[0010] The three-speed hydraulic cylinders in the above patents all achieve the positioning of the middle position by setting a step in the liquid cavity and using the step in the liquid cavity to block the movement of the piston. In the long run, the piston and the step will be deformed due to collision, resulting in large resistance to piston movement, inaccurate middle positioning, and even the problem of not being able to engage or disengage the gear. In addition, the liquid cavity with steps has a complex structure, is difficult to process, and has high production costs. In addition, the areas on both sides of the piston are different, and the hydraulic pressure when the piston is balanced is difficult to control. Summary of the invention

[0011] The technical problem to be solved by the present invention is to provide a three-speed hydraulic cylinder in view of the defects existing in the prior art.

[0012] In order to solve the above technical problems, the technical solution adopted by the present invention is: a three-gear hydraulic cylinder gear positioning method, which uses a limit device to block the piston to perform intermediate gear positioning; at the same time, the pressure difference on both sides of the piston is controlled to reduce the axial force of the piston, avoid or reduce the elastic deformation and plastic deformation between the piston and the limit ring, so as to improve the positioning accuracy of the intermediate gear.

[0013] Furthermore, a balancing flow channel is provided between adjacent liquid chambers, and the hydraulic medium maintains a stable flow between adjacent liquid chambers through the balancing flow channel, so that a stable pressure difference is formed between adjacent liquid chambers, thereby controlling the pressure difference between liquid chamber one and liquid chamber two within a predetermined range.

[0014] Furthermore, by setting a limit ring 2 at the middle gear position in the cylinder hole, and setting two pistons on both sides of the limit ring 2, the two pistons divide the cylinder hole into three liquid chambers, and by controlling the medium pressure in the three liquid chambers, the piston rod is kept in the middle gear position; at the same time, the position of the piston rod is detected by the gear sensor, and the feedback signal of the sensor is used to control the flow direction of the hydraulic medium, thereby controlling the pressure difference on both sides of the piston to achieve precise positioning of the gear.

[0015] A three-speed hydraulic cylinder comprises a cylinder body and a piston. The cylinder body comprises a guide sleeve, a cylinder barrel and an end cover. The cylinder barrel is provided with a cylindrical cylinder hole. The guide sleeve and the end cover are connected to the two ends of the cylinder barrel along the axial direction of the cylinder hole so that the cylinder hole is closed to form a liquid cavity. Liquid through port 2 and liquid through port 3 are provided on the hole walls at the two ends of the cylinder hole. The cylinder hole is a through hole with a constant diameter. A limiting ring 2 is arranged on the hole wall in the middle of the cylinder hole. A liquid passage 1 is also arranged on the hole wall of the cylinder hole. The liquid passage 1 is connected to the cylinder hole positioning groove. The piston is composed of a piston rod, an inner piston, an outer piston 1 and an outer piston 2. The inner piston is sealed and fixed on the piston rod. The outer piston 1 and the outer piston 2 are coaxially arranged on the outer periphery of the inner piston. The inner rings of the outer piston 1 and the outer piston 2 are sealed and slidably connected with the outer periphery of the inner piston. The outer piston 1 and the outer piston 2 are located on both sides of the limiting ring 2. The outer piston 1 and the outer piston 2 can slide axially along the outer periphery of the inner piston on both sides of the limiting ring 2. A balancing flow channel is arranged on the outer peripheral surface of the outer piston 1 and the outer piston 2 and between the cylinder hole. The hydraulic medium maintains a stable flow between adjacent liquid cavities through the balancing flow channel, so that a stable pressure difference is formed between adjacent liquid cavities, so that the pressure difference between the liquid cavity 1 and the liquid cavity 2 is controlled within a predetermined range. To reduce the axial force of the piston, avoid the piston hitting the limit ring 2 to cause displacement, reduce the elastic deformation and plastic deformation between the piston and the limit ring 2, so as to improve the positioning accuracy of the intermediate gear.

[0016] Furthermore, an annular cylinder hole positioning groove is provided in the middle of the hole wall of the cylinder hole, and the second limiting ring is clamped in the cylinder hole positioning groove. The second limiting ring adopts a clamping method, which simplifies the processing technology of the cylinder hole, reduces the cost, and facilitates the installation and replacement of the second limiting ring.

[0017] Furthermore, a limiting ring 1 is arranged at the middle part of the outer circumference of the inner piston, and the outer piston 1 and the outer piston 2 are arranged on both sides of the limiting ring 1 respectively.

[0018] Furthermore, a piston positioning groove is arranged on the outer circumference of the inner piston, and the limiting ring 1 is clamped in the piston positioning groove. The limiting ring 1 adopts a clamping method, which is convenient for the installation and replacement of the limiting ring 1.

[0019] Furthermore, the balance flow channel is the gap between the outer circumference of the outer piston 1 and the outer piston 2 and the cylinder hole. The hydraulic medium maintains a stable flow between adjacent liquid chambers through the balance flow channel, so that a stable pressure difference is formed between adjacent liquid chambers, so that the pressure difference between liquid chamber 1 and liquid chamber 2 is controlled within a predetermined range, so as to reduce the axial force of the piston, avoid elastic deformation and plastic deformation caused by the piston hitting the limit ring 2, and improve the positioning accuracy of the intermediate gear. At the same time, the hydraulic medium can also ensure the lubrication between the outer circumference of the outer piston 1 and the outer piston 2 and the cylinder hole.

[0020] Furthermore, the balancing flow channel also includes grooves on the outer peripheral surfaces of the outer piston 1 and the outer piston 2, and the grooves are multiple annular grooves or spiral grooves.

[0021] Furthermore, one end of the piston rod is connected to a gear position sensor, and the feedback signal of the sensor is used to control the flow direction of the hydraulic medium, thereby controlling the pressure difference on both sides of the piston to achieve accurate positioning of the gear position.

[0022] The beneficial effects of the present invention are as follows: a clamping limit ring is arranged in the middle of the bore wall of the cylinder hole to simplify the processing of the cylinder hole and reduce the processing cost. At the same time, a combined piston is adopted, and a balance flow channel is arranged between the outer peripheral surface of the piston and the cylinder hole. The hydraulic medium maintains a stable flow between adjacent liquid chambers through the balance flow channel, thereby controlling the pressure difference on both sides of the piston to reduce the axial force of the piston, avoid displacement caused by the piston hitting the limit ring, reduce the elastic deformation and plastic deformation between the piston and the limit ring, and improve the positioning accuracy of the intermediate gear. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the three-dimensional structure of a three-dimensional hydraulic cylinder.

[0024] Figure 2 It is a schematic diagram of the three-dimensional structure of the cylinder.

[0025] Figure 3 This is a front view of the cylinder body.

[0026] Figure 4 for Figure 3 Middle AA section view,

[0027] Figure 5 for Figure 4 The cross-sectional view after the second limit ring is installed.

[0028] Figure 6 It is a cross-sectional schematic diagram of the cylinder 3,

[0029] Figure 7 It is a schematic diagram of the three-dimensional structure of the piston rod 1 and the combined piston.

[0030] Figure 8It is a front view schematic diagram of the piston rod 1 and the combined piston embodiment 1,

[0031] Fig. 9 It is a front view schematic diagram of the piston rod 1 and the combined piston embodiment 2,

[0032] Fig.10 It is a side view of the piston rod 1 and the combined piston,

[0033] Fig.11 for Fig.10 Middle BB section view (state 1),

[0034] Fig.12 for Fig.10 Middle BB section view (state 2),

[0035] Fig.13 for Fig.10 Middle BB section view (state 3),

[0036] Fig.14 is a cross-sectional view of the piston rod 1,

[0037] Fig.15 is a cross-sectional view of the inner piston 4,

[0038] Fig.16 This is a cross-sectional diagram of the three-speed hydraulic cylinder in the middle position.

[0039] Fig.17 This is a cross-sectional diagram of the three-speed hydraulic cylinder moving to the right.

[0040] Fig.18 This is a cross-sectional diagram of the three-speed hydraulic cylinder moving to the right limit position.

[0041] Fig.19 This is a cross-sectional diagram of the three-speed hydraulic cylinder moving to the left.

[0042] Fig. 20 This is a cross-sectional diagram of the three-speed hydraulic cylinder moving to the left to the limit position.

[0043] In the figure: 1-piston rod, 101-fork fixing hole, 102-piston card slot, 103-sealing ring slot, 104-pin hole, 2-guide sleeve, 3-cylinder, 301-cylinder hole, 302-cylinder hole positioning slot, 303-stop, 304-card slot, 4-inner piston, 401-inner piston component 1, 402-inner piston component 2, 403-piston convex edge, 404-piston positioning slot, 5-outer piston 1, 6-limiting ring 1, 7-limiting ring 2, 8—liquid port 1, 9—external piston 2, 10—end cover, 11—bolt, 12—sensor, 13—sensor block, 14—pin, 15—sealing ring, 16—elastic retaining ring, 17—liquid chamber 1, 18—liquid port 2, 19—balance flow channel, 20—liquid chamber 2, 21—liquid port 3, 22—liquid chamber 3, L1—distance between the pin and the end face of the cylinder body in the middle gear, L2—distance between the pin and the end face of the cylinder body in the right gear, L3—distance between the pin and the end face of the cylinder body in the left gear. DETAILED DESCRIPTION

[0044] The present invention will be further described below through specific embodiments and in conjunction with the accompanying drawings:

[0045] like Figure 1 As shown: the three-speed hydraulic cylinder includes a cylinder body, a piston and a sensor. The piston can slide in the cylinder body. The sensor is connected to one end of the piston rod to detect the position of the piston rod.

[0046] Cylinder body Figures 2 to 5 As shown: the cylinder body includes a guide sleeve 2, a cylinder barrel 3 and an end cover 10. The cylinder barrel 3 is provided with a cylindrical cylinder hole 301. The guide sleeve 2 and the end cover 10 are connected to the two ends of the cylinder barrel 3 along the axial direction of the cylinder hole 301, so that the cylinder hole 301 is closed to form a liquid cavity. The hole wall at both ends of the cylinder hole 301 is provided with a second liquid passage 18 and a third liquid passage 21. The cylinder hole 301 is a through hole with a constant diameter. An annular cylinder hole positioning groove 302 is provided in the middle of the hole wall of the cylinder hole 301.

[0047] The limiting ring 27 is a metal ring with an opening. The compressed limiting ring 27 is placed in the cylinder hole 301, and the limiting ring 27 is moved to the cylinder hole positioning groove 302, and the limiting ring 27 is inserted into the cylinder hole positioning groove 302. The inner ring diameter of the limiting ring 27 is smaller than the diameter of the cylinder hole 301 and the piston, and can be used to block the piston and play a limiting role. A liquid port 18 is also provided on the wall of the cylinder hole 301, and the liquid port 18 is connected to the cylinder hole positioning groove 302.

[0048] Cylinder 3 Figure 6As shown in the figure, the two ends of the cylinder hole 301 are provided with stoppers 303, and the outer sides of the stoppers 303 at both ends are also provided with clamping grooves 304. The guide sleeve 2 and the end cover 10 are inserted into the cylinder hole 301 from both ends of the cylinder barrel 3, and the guide sleeve 2 and the end cover 10 are positioned by the stoppers 303, and then the guide sleeve 2 and the end cover 10 are clamped to the two ends of the cylinder barrel 3 by the elastic retaining ring 16. This clamping method has a simple structure and is easy to install.

[0049] Piston Figures 7 to 10 As shown: the piston is composed of a piston rod 1, an inner piston 4, an outer piston 1 5 and an outer piston 2 9, and the inner piston 4 is sealed and fixed on the piston rod 1. A piston positioning groove 404 is provided in the middle of the outer circumference of the inner piston 4, and a limit ring 1 6 is clamped in the piston positioning groove 404. The outer piston 1 5 and the outer piston 2 9 are coaxially arranged on the outer circumference of the inner piston 4, and are arranged on both sides of the limit ring 1 6. Multiple annular grooves or spiral grooves with semicircular cross-sections are provided on the outer circumferences of the outer piston 1 5 and the outer piston 2 9.

[0050] like Figures 11 to 13 As shown in the figure, the inner rings of the outer piston 1 5 and the outer piston 2 9 are sealed and slidably connected with the outer periphery of the inner piston 4, and the outer piston 1 5 and the outer piston 2 9 can slide axially along the outer periphery of the inner piston 4 on both sides of the limiting ring 2 7. The limiting ring 2 7 is used to limit the movement range of the outer piston 1 5 and the outer piston 2 9 to control the movement position of the piston rod 1 and realize the gear positioning.

[0051] Piston rod 1 Fig.14 As shown: a fork fixing hole 101 is provided at one end of the piston rod 1 for installing the fork; a pin hole 104 is provided at the other end of the piston rod 1 for inserting the pin 14 and connecting with the sensor shift block 13; a piston clamping groove 102 and a sealing ring groove 103 are provided in the middle of the piston rod 1, and a sealing ring is clamped in the sealing ring groove 103. When the piston rod 1 is inserted into the center hole of the inner piston 4, the two piston clamping grooves 102 are located at both ends of the center hole of the piston 4, and then the inner piston 4 is clamped on the piston rod 1 with an elastic retaining ring 16. This clamping method has a simple structure and is easy to install.

[0052] Inner piston 4 Fig.15As shown: it is composed of an inner piston assembly 1 401 and an inner piston assembly 2 402. A piston positioning groove 404 is provided in the middle of the inner piston assembly 1 401 for clamping the limit ring 1 6. The limit ring 1 6 adopts a metal ring with an opening. The expanded limit ring 1 6 is put on the inner piston assembly 1 401, and the limit ring 1 6 is moved to the piston positioning groove 404, and the limit ring 1 6 is clamped into the piston positioning groove 404. The outer diameter of the limit ring 1 6 is larger than the inner diameter of the outer piston 1 5 and the outer piston 2 9, and can control the sliding range of the outer piston 1 5 and the outer piston 2 9 for limiting. When the outer piston 1 5 and the outer piston 2 9 are pushed by the hydraulic medium to encounter the limit ring 1 6, the limit ring 1 6 can transfer the pressure of the hydraulic medium on the outer piston 1 5 and the outer piston 2 9 to the inner piston 4. The edges of the inner piston assembly 401 and the inner piston assembly 402 are provided with piston convex edges 403, which are used to transfer the pressure of the hydraulic medium exerted on the outer piston 1 5 and the outer piston 2 9 to the inner piston 4, and at the same time can control the sliding range of the outer piston 1 5 and the outer piston 2 9.

[0053] When the three-speed hydraulic cylinder is in the middle gear Fig.16 As shown: a limiting ring 27 is arranged in the middle of the cylinder hole 301 of the three-speed hydraulic cylinder, and an outer piston 15 and an outer piston 29 are arranged on both sides of the limiting ring 16 and the limiting ring 27. The inner piston 4, the outer piston 15 and the outer piston 29 divide the cylinder hole 301 into three liquid chambers: liquid chamber 17, liquid chamber 20 and liquid chamber 3 22. The three liquid chambers are connected to the hydraulic power source through the liquid port 2 18, the liquid port 18 and the liquid port 3 21 respectively. Different from the existing three-position hydraulic cylinder in which a sealing ring is arranged between the cylinder hole and the piston, there is no sealing device between the inner wall of the cylinder hole 301 and the outer periphery of the outer piston 15 and the outer piston 29 in the present invention, and a gap is left between the inner wall of the cylinder hole 301 and the outer periphery of the outer piston 15 and the outer piston 29 as a balance flow channel 19. When there is a pressure difference between the medium pressures in adjacent liquid chambers, the pressure difference pushes the piston to move, and the medium in the liquid chamber will also flow to the liquid chamber with low pressure through the balance flow channel 19. When the medium flows through the balancing flow channel 19, the medium pressure needs to overcome the flow resistance of the balancing flow channel 19. When the pressure difference in adjacent liquid chambers is equal to the flow resistance of the balancing flow channel 19, a stable pressure difference is maintained between adjacent liquid chambers, and a stable liquid flow is maintained in the balancing flow channel 19. In order to control the pressure difference in adjacent liquid chambers, the flow area of ​​the balancing flow channel 19 needs to be adjusted, so a plurality of annular grooves or spiral grooves with semicircular cross-sections are provided on the outer circumference of the outer piston 1 5 and the outer piston 2 9.

[0054] exist Fig.16In the process, the pressure medium is filled into the liquid chamber 17 through the liquid port 2 18, the pressure medium is filled into the liquid chamber 3 22 through the liquid port 3 21, and the medium in the liquid chamber 20 is discharged and depressurized through the liquid port 1 8. There is a pressure difference between the liquid chamber 17 and the liquid chamber 20, and the medium pressure pushes the outer piston 1 5 to the middle position. When the outer piston 1 5 is blocked by the limit ring 2 7, the outer piston 1 5 stops moving; during this process, the outer piston 1 5 may push the inner piston 4 and the piston rod 1 to the middle position through the limit ring 1 6. At the same time, the medium pressure also pushes the outer piston 2 9 to the middle position. When the outer piston 2 9 is blocked by the limit ring 2 7, the outer piston 2 9 stops moving; during this process, the outer piston 2 9 may push the inner piston 4 and the piston rod 1 to the middle position through the limit ring 1 6, thereby pushing the piston rod 1 to the middle gear. At the same time, the sensor block 13 is driven to rotate with one end of the piston rod 1 through the pin 14, so that the sensor 12 rotates and remains in the middle gear position, and the distance between the pin 14 and the end face of the cylinder body is L1. The sensor 12 transmits the gear position to the display remotely, and at the same time, the pressure in the liquid chamber 1 17 and the liquid chamber 3 22 is maintained through the solenoid valve, so that the liquid chamber 2 20 is in a pressure relief state.

[0055] Since the balance flow channel 19 is passed between the liquid chamber 1 17 and the liquid chamber 2 20, and between the liquid chamber 3 22 and the liquid chamber 2 20, the medium in the liquid chamber 1 17 and the liquid chamber 3 22 flows to the liquid chamber 2 20 through the balance flow channel 19. In the process of the medium continuously and stably flowing through the balance flow channel 19, a stable pressure difference will be formed between the liquid chamber 1 17 and the liquid chamber 2 20, and between the liquid chamber 3 22 and the liquid chamber 2 20, so that the inner piston 4 and the piston rod 1 are subjected to two opposite axial forces from the outer piston 1 5 and the outer piston 2 9, so that the inner piston 4 and the piston rod 1 are kept in the middle gear. Since the medium flows stably in the balance flow channel 19, it can not only control the pressure difference between adjacent liquid chambers, but also play a role in lubrication and cooling.

[0056] The shifting process of the three-speed hydraulic cylinder from the middle gear to the right gear is as follows Fig.17 and 18As shown: the pressure medium is filled into the liquid chamber 17 through the liquid port 2 18, and the medium in the liquid chamber 3 22 and the liquid chamber 2 20 is discharged and depressurized through the liquid port 3 21 and the liquid port 1 8. There is a pressure difference between the liquid chamber 17 and the liquid chamber 2 20 and the liquid chamber 3 22, and the medium pressure pushes the outer piston 1 5 and the inner piston 4 toward the end cover 10. When the outer piston 1 5 is blocked by the limit ring 2 7, the outer piston 1 5 stops moving. At the same time, the medium pressure acting on the inner piston 4 continues to push the inner piston 4 toward the end cover 10. At the same time, the inner piston 4 pushes the outer piston 2 9 toward the end cover 10 through the limit ring 1 6. When the outer piston 2 9 hits the end cover 10, the inner piston 4 and the piston rod 1 will stop moving. At the same time, the sensor shift block 13 is driven to rotate through the pin 14 at one end of the piston rod 1, so that the sensor 12 rotates and remains in the right gear position, and the distance between the pin 14 and the cylinder end face is L2. The sensor 12 detects whether the piston rod 1 reaches the right limit position. After reaching the right limit position, it transmits an electrical signal to control the solenoid valve to stop pressurizing, and the piston rod 1 completes the right shift and remains in the right gear position.

[0057] The shifting process of the three-speed hydraulic cylinder from the middle gear to the left gear is as follows Fig.19 and 20 As shown: the liquid port 3 21 fills the liquid chamber 3 22 with pressure medium, and at the same time, the medium in the liquid chamber 17 and the liquid chamber 2 20 is discharged and depressurized through the liquid port 2 18 and the liquid port 1 8. There is a pressure difference between the liquid chamber 3 22 and the liquid chamber 2 20 and the liquid chamber 1 17, and the medium pressure pushes the outer piston 2 9 and the inner piston 4 toward the guide sleeve 2. When the outer piston 2 9 is blocked by the limit ring 2 7, the outer piston 2 9 stops moving. At the same time, the medium pressure acting on the inner piston 4 continues to push the inner piston 4 toward the guide sleeve 2. At the same time, the inner piston 4 pushes the outer piston 1 5 toward the guide sleeve 2 through the limit ring 1 6. When the outer piston 1 5 hits the guide sleeve 2, the inner piston 4 and the piston rod 1 will stop moving. At the same time, the sensor shift block 13 is driven to rotate with one end of the piston rod 1 through the pin 14, so that the sensor 12 rotates and remains in the left gear position, and the distance between the pin 14 and the cylinder end face is L3. The sensor 12 detects whether the piston rod 1 reaches the left limit position. After reaching the left limit position, it transmits an electrical signal to control the solenoid valve to stop pressurizing, and the piston rod 1 completes the left shift and remains in the left gear position.

[0058] In summary, the beneficial effects of the present invention are as follows: a clamping limit ring is provided in the middle of the bore wall of the cylinder hole to simplify the processing of the cylinder hole and reduce the processing cost. At the same time, a combined piston is adopted, and a balance flow channel is provided between the outer peripheral surface of the piston and the cylinder hole. The hydraulic medium maintains a stable flow between adjacent liquid chambers through the balance flow channel, thereby controlling the pressure difference on both sides of the piston to reduce the axial force of the piston, avoid displacement caused by the piston hitting the limit ring, reduce the elastic deformation and plastic deformation between the piston and the limit ring, and improve the positioning accuracy of the intermediate gear.

[0059] The above embodiments are only used to illustrate the present invention, rather than to limit the present invention. Technicians in the relevant technical field may make various changes or modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions should also fall within the protection scope of the present invention, and the protection scope of the present invention should be defined by the claims.

Claims

1. A three-speed hydraulic cylinder, comprising a cylinder body and a piston, wherein the cylinder body comprises a guide sleeve (2), a cylinder barrel (3), an end cover (10) and a piston, wherein the cylinder barrel (3) is provided with a cylindrical cylinder hole (301), the guide sleeve (2) and the end cover (10) are connected to the two ends of the cylinder barrel (3) along the axial direction of the cylinder hole (301), so that the cylinder hole (301) is closed to form a liquid cavity, and a second liquid passage port (18) and a third liquid passage port (21) are provided on the hole walls at the two ends of the cylinder hole (301); characterized in that The cylinder hole (301) is a through hole with a constant diameter. A limiting ring (2) (7) is arranged on the hole wall in the middle of the cylinder hole (301). A liquid passage (1) (8) is also arranged on the hole wall of the cylinder hole (301). The liquid passage (1) (8) is connected to the cylinder hole positioning groove (302). The piston is composed of a piston rod (1), an inner piston (4), an outer piston (1) (5) and an outer piston (2) (9). The inner piston (4) is sealed and fixed on the piston rod (1). The outer piston (1) (5) and the outer piston (2) (9) are coaxially arranged on the outer periphery of the inner piston (4) and are sealed and slidably connected (5) with the outer periphery of the inner piston (4). The outer piston (1) (5) and the outer piston (2) (9) can slide axially along the outer periphery of the inner piston (4) on both sides of the limiting ring (2) (7) to divide the cylinder hole (301) into three parts. The invention relates to a liquid cavity, wherein the limit ring 2 (7) is used to limit the movement range of the outer piston 1 (5) and the outer piston 2 (9) to control the movement position of the piston rod (1); a balancing flow channel (19) is provided between the outer peripheral surface of the outer piston 1 (5) and the outer piston 2 (9) and the cylinder hole (301); the balancing flow channel (19) is the gap between the outer peripheral surface of the outer piston 1 (5) and the outer piston 2 (9) and the cylinder hole (301); the balancing flow channel (19) includes grooves on the outer peripheral surface of the outer piston 1 (5) and the outer piston 2 (9), and the grooves are multiple annular grooves or spiral grooves; by controlling the medium pressure in the three liquid cavities, the pressure difference on both sides of the piston is controlled to achieve accurate positioning of the gear, and the feedback signal of the sensor (12) is used to control the flow direction of the hydraulic medium.

2. The three-speed hydraulic cylinder according to claim 1 is characterized in that An annular cylinder hole positioning groove (302) is provided in the middle of the hole wall of the cylinder (301), and the second limiting ring (7) is clamped in the cylinder hole positioning groove (302).

3. The three-speed hydraulic cylinder according to claim 2 is characterized in that A limiting ring (6) is arranged at the middle of the outer circumference of the inner piston (4), and an outer piston (5) and an outer piston (9) are arranged on both sides of the limiting ring (6) respectively.

4. The three-speed hydraulic cylinder according to claim 3 is characterized in that A piston positioning groove (404) is provided on the outer periphery of the inner piston (4), and a limiting ring (6) is clamped in the piston positioning groove (402).

5. The three-speed hydraulic cylinder according to any one of claims 1 to 4, characterized in that One end of the piston rod (1) is connected to the gear position sensor (12).

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