A control valve for a constant power piston pump

Abstract

A control valve for a constant power piston pump according to the present invention includes a valve body, a valve sleeve installed in the valve body, and a valve core nested and connected in the valve sleeve; one end of the valve core abuts against a pilot valve core, and a spring loading device is provided at the other end; the spring loading device can provide a spring force to the valve core for adjusting the power setting value of the piston pump; the pilot valve core is connected to the pressure oil output by a proportional valve through a two-position four-way directional control valve, and different pressures are output by the proportional valve to achieve variable power control; the valve core cooperates with the valve sleeve, and the valve core acts against the spring force of the spring loading device under the combined action of the outlet pressure oil and the pilot valve core, gradually opening the passage for the hydraulic oil to flow to the variable piston chamber of the piston pump, so that the variable piston pushes the swash plate of the piston pump under the action of the hydraulic oil. The present invention can solve the problem of power loss caused by the inconsistency between the inflection point of the actual output constant power curve and the theoretical constant power inflection point existing in the prior art.

Description

Technical Field

[0001] The present invention relates to the field of hydraulic pumps, and more particularly to a control valve for a constant power piston pump. Background Art

[0002] Currently, the hydraulic power sources of domestic and foreign excavators generally adopt constant power control piston pumps, aiming to adjust the flow output of the pump according to the outlet pressure, so that the product of the pump's output flow and pressure remains approximately constant, and make full use of the engine power to achieve energy-saving effects.

[0003] Analyzing the existing constant power piston pump regulators, they adopt a double-spring structure with different lengths, and use a double broken line to approximate and fit a hyperbola. During the pressure increase process, first compress the large spring, and then compress the large and small springs simultaneously, generating a P-Q double broken line as shown in Curve a in Figure 1 . The theoretical constant power curve is an inverse function curve, as shown in Curve 1 in the appendix Figure 1 .

[0004] By comparing the curves in the appendix Figure 1 , it can be seen that only in the S mode, the actual power starting point is approximately equal to the theoretical value. In the H mode, the actual power starting point is larger than the theoretical value, which requires the engine to have sufficient power margin, otherwise it will cause the engine to stall. In the L mode, the actual power starting point is smaller than the theoretical value, which will result in the inability to fully utilize the engine power and cause power loss.

[0005] Secondly, when implementing the power mode switching function, the existing structure directly uses the pressure oil output by the proportional valve to act on the non-step valve core. By changing the output current of the proportional valve, the output pressure is changed to achieve variable power control. The problem of whether the power values in different modes required by the host can be matched based on the existing proportional valve output characteristics (there are differences from the benchmark output characteristics) without changing the input current is not considered. Due to the differences in the proportional valve output characteristics of different manufacturers, if the existing structure is used to match the power values that meet the requirements of the host factory, the selectable range of the proportional valve will be reduced, increasing the product cost.

[0006] To solve the problems of power loss caused by the inconsistency between the inflection points of the actual output constant power curve and the theoretical constant power inflection point in the existing technology and expanding the selectable range of the proportional valve to reduce the product cost, a control valve for a constant power piston pump is urgently needed. Summary of the Invention

[0007] The purpose of the present invention is to overcome the deficiencies in the existing technology and provide a control valve for a constant power piston pump to solve the problem of power loss caused by the inconsistency between the inflection points of the actual output constant power curve and the theoretical constant power inflection point in the existing technology.

[0008] To achieve the above object, the present invention is implemented by the following technical solutions:

[0009] The present invention provides a control valve for a constant power piston pump, comprising a valve body, a valve sleeve installed in the valve body, and a valve core nested and connected in the valve sleeve;

[0010] One end of the valve core abuts against the pilot valve core, and the other end is provided with a spring loading device;

[0011] The spring loading device can provide a spring force to the valve core for adjusting the power setting value of the piston pump;

[0012] The pilot valve core is connected to the pressure oil output by the proportional valve through a two-position four-way reversing valve. By using different pressures output by the proportional valve, variable power control is achieved; the valve core cooperates with the valve sleeve. The valve core acts under the combined action of the outlet pressure oil and the pilot valve core to overcome the spring force of the spring loading device, and gradually opens the channel for the hydraulic oil to flow to the variable piston chamber of the piston pump, so that the variable piston pushes the swash plate of the piston pump under the action of the hydraulic oil;

[0013] A feedback rod pin, a feedback rod and a fulcrum pin are connected to the valve sleeve. One end of the feedback rod rotates around the fulcrum pin, and the other end is connected to the variable piston of the piston pump. When the variable piston moves, the feedback rod pin on the feedback rod drives the valve sleeve to move, gradually closing the channel for the hydraulic oil to flow to the variable piston chamber of the piston pump;

[0014] When the hydraulic oil at the pump outlet reaches the set value, the valve core moves under the action of the force generated by the area difference and the force generated by the pilot valve core to overcome the spring force of the spring loading device. The channel for the hydraulic oil to flow to the variable piston chamber of the piston pump is connected, and the hydraulic oil flows to the variable piston chamber of the piston pump. The variable piston pushes the swash plate to change the swing angle under the action of the hydraulic oil to realize the change of the pump output flow. When the variable piston moves, it rotates around the fulcrum pin through the feedback rod, and drives the valve sleeve to move leftward through the feedback rod pin, controlling the opening size of the channel for the hydraulic oil to flow to the variable piston chamber of the piston pump, so as to ensure that the product of the flow rate and the outlet pressure at the pump outlet is approximately constant.

[0015] Further, the control valve for the constant power piston pump further includes a cover plate and an end cover.

[0016] Further, the pilot valve core is provided with a structure of two different diameters and is installed in the cover plate;

[0017] By adjusting the screwing depth of the reversing valve spring adjusting rod, the pre-tightening force of the reversing valve spring is adjusted, and whether the two-position four-way reversing valve core changes direction is controlled, thereby controlling the effective acting area of the pilot oil acting on the pilot valve core;

[0018] The two-position four-way directional control valve is used to switch the flow state of the hydraulic oil flowing into the pilot valve spool. When the two-position four-way directional control valve spool is in the right position, the hydraulic oil acts on two stepped surfaces of the pilot valve spool. When it is in the left position, the hydraulic oil acts on one stepped surface of the pilot valve spool.

[0019] Further, the two-position four-way directional control valve includes a directional control valve spring adjusting rod, a directional control valve spring seat, a directional control valve spring, and a two-position four-way directional control valve spool. The two-position four-way directional control valve is used to switch the flow state of the hydraulic oil flowing into the pilot valve spool 4. When the two-position four-way directional control valve spool is in the right position, the hydraulic oil acts on two stepped surfaces of the pilot valve spool 4. When it is in the left position, the hydraulic oil acts on one stepped surface of the pilot valve spool 4.

[0020] The two-position four-way directional control valve spool is installed in the cover plate. The two-position four-way directional control valve spool is provided with an axial hole and a radial hole for leading the hydraulic oil to the small end of the two-position four-way directional control valve spool.

[0021] The large end face of the two-position four-way directional control valve spool is connected to the directional control valve spring. The directional control valve spring is installed on the spring seat. The other end of the spring seat is connected to the directional control valve spring adjusting rod. The directional control valve spring adjusting rod is installed on the end cover with a threaded hole and fixed by a lock nut. The end cover is installed on the cover plate.

[0022] Further, an O-ring groove for installing an O-ring is provided on the two-position four-way directional control valve spool to prevent the hydraulic oil from entering the spring cavity.

[0023] Further, the pilot valve spool is provided with a structure with two different diameters and is installed in the cover plate. By adjusting the screwing depth of the directional control valve spring adjusting rod, the pre-tightening force of the directional control valve spring is adjusted, and whether the two-position four-way directional control valve spool is switched is controlled, so as to control the effective acting area of the pilot oil acting on the pilot valve spool.

[0024] Further, the spring loading device includes a spring seat, a high-power spring, a low-power spring, a high-power spring adjusting seat, a low-power spring adjusting rod, a lock nut, a high-power spring lock nut, and a spring adjusting cover plate.

[0025] A spring cavity is provided on the valve body. The spring seat, the high-power spring, the low-power spring installed in the high-power spring, the high-power spring adjusting seat, and the low-power spring adjusting rod are installed in the spring cavity.

[0026] The spring adjusting cover plate is used to fix the high-power spring adjusting seat. The high-power spring adjusting seat is used to install the high-power spring and the low-power spring adjusting rod. By adjusting the high-power spring adjusting seat, the first inflection point of the power curve is changed. After adjustment, it is locked with the high-power spring lock nut. The low-power spring adjusting rod is used to install the low-power spring and adjust the second inflection point of the power curve. After adjustment, it is locked with the lock nut. The spring seat is used to transmit the acting force of the valve spool to the spring.

[0027] Further, the inner hole of the valve sleeve is provided with structures of different diameters.

[0028] The valve core is provided with structures of different diameters that match the valve sleeve and is installed inside the valve sleeve 2.

[0029] Further, the inner hole of the valve sleeve 2 is provided with structures of three different diameters d1, d2, and d3. The valve core is provided with three structures of different diameters that match the valve sleeve and is installed inside the valve sleeve.

[0030] Further, the valve body 1 is provided with oil ports and flow channels.

[0031] The valve sleeve 2 is installed inside the valve body 1 to form a P1 chamber, a P2 chamber, an A chamber, and a T chamber.

[0032] The P2 chamber is used to introduce the pump outlet pressure, which thus acts on the valve core with the annular areas of d2 and d3. The T chamber is used for pressure relief. The P1 chamber is used to introduce the pump outlet pressure, which thus acts on the valve core with the annular areas of d1 and d2. The movement of the valve core will cause the A chamber to communicate with the variable piston chamber.

[0033] In a second aspect, the present invention provides a method for using a control valve for a constant power piston pump as described in the first aspect, including the following steps:

[0034] The excavator is equipped with three modes: H heavy load, S standard, and L normal.

[0035] In the H or S mode, by adjusting the screwing depth of the reversing valve spring adjusting rod to adjust the pre-tightening force of the reversing valve spring, the pilot valve core cannot overcome the spring force to move under the action of the control oil Pf. When the hydraulic oil at the pump outlet reaches the set value, the valve core moves leftward under the action of the force generated by the area difference and the force generated by the pilot valve core, overcoming the spring force of the high-power spring. The hydraulic oil flows to the variable piston chamber of the piston pump. The variable piston pushes the swash plate to change the swing angle under the action of the hydraulic oil to realize the change of the pump output flow. While the swash plate swings, it rotates around the fulcrum pin through the feedback rod, and drives the valve sleeve to move leftward through the feedback rod pin, controlling the opening size between the P1 chamber and the A chamber, so as to ensure that the product of the flow rate and the outlet pressure at the pump outlet is approximately constant, forming the first variable characteristic curve. By adjusting the diameters d4 and d5 of the matching power pilot valve core, the actual power inflection point can be made to coincide with the theoretical power inflection point. When the pump outlet pressure rises to a certain value, the low-power spring also generates a force, forming the second variable characteristic curve.

[0036] In the L mode, the force exerted by the increasing control oil pressure Pf on the pilot spool overcomes the spring force and causes it to move leftward. The oil acting on the 4-step surface of the pilot spool flows back to the T port through the Pf1 passage and the two-position four-way reversing spool 11 for pressure relief, and a part of the control oil acts on the 4d5-step surface of the pilot spool. As the pump outlet pressure increases, the spool 3 moves under the action of the force generated by the area difference and the force generated by the pilot spool 4, achieving constant power control in this mode. Since the force-bearing area of the pilot spool 4 becomes smaller, the force acting on the spool 3 decreases accordingly. Thus, under the same pilot control oil condition, the pump outlet pressure corresponding to the first inflection point of constant power is higher than that of a single-stage spool and is closer to the inflection point corresponding to the theoretical power.

[0037] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0038] (1) It effectively avoids the problem that the engine power cannot be fully utilized, achieving an energy-saving effect;

[0039] (2) It effectively avoids the problem that the output characteristics of the existing proportional valve cannot match the power values required by the OEM in different modes, expands the selection range of proportional valves, and reduces product costs;

[0040] (3) The spool structure is simple, easy to machine, and convenient for assembly. Description of the Drawings

[0041] Figure 1 It is a schematic diagram of the change of the P-Q curve of the existing structure

[0042] Figure 2 It is a structural diagram of the control valve for a constant power piston pump

[0043] Figure 3 It is a structural diagram of the two-position four-way reversing spool

[0044] Figure 4 It is a structural diagram of the pilot spool

[0045] Figure 5 It is a structural diagram of the cover plate

[0046] Figure 6 It is a system schematic diagram;

[0047] Figure 7 It is a schematic diagram of the valve sleeve and the spool;

[0048] Figure 8 It is a schematic diagram of the feedback connection structure of the piston pump;

[0049] Figure 9 It is a schematic diagram of the inflection point of the power curve.

[0050] In the figure: 1, valve body; 2, valve sleeve; 3, valve core; 4, pilot valve core; 5, cover plate; 6, end cover; 7 (7-1, 7-2), lock nut; 8, reversing valve spring adjusting rod; 9, reversing valve spring seat; 10, reversing valve spring; 11, two-position four-way reversing valve core; 12, feedback rod; 13, spring seat; 14, large power spring; 15, small power spring; 16, small power spring adjusting rod; 17, feedback rod pin; 18, large power spring adjusting seat; 19, large power spring lock nut; 20 (20-1 to 20-5), O-ring; 21, fulcrum pin; 22, spring adjusting cover plate. Specific implementation mode

[0051] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0052] In the description of this embodiment, it should be noted that terms such as "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing this embodiment and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, so it cannot be understood as a limitation to this embodiment.

[0053] This embodiment provides a control valve for a constant power piston pump to solve the problems of power loss caused by the inconsistency between the inflection point of the actual output constant power curve and the theoretical constant power inflection point in the prior art, and to expand the optional range of the proportional valve and reduce the product cost on the premise of meeting the power values in different modes required by the main engine.

[0054] This invention patent adopts the Figure 2 structure shown in the figure, including valve body 1, valve sleeve 2, valve core 3, pilot valve core 4, cover plate 5, end cover 6, lock nut 7 (7-1, 7-2), reversing valve spring adjusting rod 8, reversing valve spring seat 9, reversing valve spring 10, two-position four-way reversing valve core 11, feedback rod 12, spring seat 13, large power spring 14, small power spring 15, small power spring adjusting rod 16, feedback rod pin 17, large power spring adjusting seat 18, large power spring lock nut 19, O-ring 20 (20-1 to 20-5), fulcrum pin 21, spring adjusting cover plate 22.

[0055] The valve body 1 is provided with P, A, T oil ports and a flow passage Pf. The valve sleeve 2 is installed in the valve body 1 to form a P1 chamber, a P2 chamber, an A chamber and a T chamber. The valve sleeve 2 is connected with a feedback rod pin 17, a feedback rod 12 and a fulcrum pin 21. The inner hole of the valve sleeve 2 has three structures with different diameters d1, d2, d3. The valve core 3 is provided with three structures with different diameters matching the valve sleeve 2 and is installed in the valve sleeve 2. One end of the valve core 3 is equipped with a spring loading device (spring seat 13, high-power spring 14, low-power spring 15, high-power spring adjusting seat 18, low-power spring adjusting rod 16, locking nut 7-2, high-power spring locking nut 19, spring adjusting cover plate 21). The other end of the valve core is provided with a pilot valve core 4 having two different diameters d4, d5. The pilot valve core 4 is installed in the cover plate 5. The cover plate 5 is provided with a Pf flow passage and a return oil T flow passage. The two-position four-way reversing valve core 11 is installed in the cover plate 5. The two-position four-way reversing valve core 11 is provided with an axial hole a1 and a radial hole a2 for leading hydraulic oil to the small end of the two-position four-way reversing valve core 11. The two-position four-way reversing valve core 11 is provided with an O-ring groove for installing an O-ring 20-1 to prevent oil from entering the spring chamber. The large end face is connected with the reversing valve spring 10. The reversing valve spring 10 is installed on the spring seat 9. The other end of the spring seat 9 is connected with the reversing valve spring adjusting rod 8. The reversing valve spring adjusting rod 8 is installed on the end cover 6 with a threaded hole and fixed by a locking nut 7-1. The end cover 6 is installed on the cover plate 5.

[0056] The control valve for a constant power piston pump includes a valve body 1, a valve sleeve 2. The valve sleeve 2 is connected with a feedback rod pin 17, a feedback rod 12 and a fulcrum pin 21. The inner hole of the valve sleeve 2 has a hole matching the valve core 3. One end of the valve core 3 is equipped with a spring loading device (spring seat 13, high-power spring 14, low-power spring 15, high-power spring adjusting seat 18, low-power spring adjusting rod 16, locking nut 7-2, high-power spring locking nut 19, spring adjusting cover plate 21). The other end of the valve core 3 has a pilot valve core 4. The pilot valve core 4 is installed in the cover plate 5. The two-position four-way reversing valve core 11 is installed in the cover plate 5. The large end face is connected with the reversing valve spring 10. The reversing valve spring 10 is installed on the spring seat 9. The other end of the spring seat 9 is connected with the reversing valve spring adjusting rod 8. The reversing valve spring adjusting rod 8 is installed on the end cover 6 with a threaded hole and fixed by a locking nut 7-1. The end cover 6 is installed on the cover plate 5.

[0057] The valve body is provided with a cavity for installing the valve sleeve 2 and is provided with P, A, T oil ports and a flow passage Pf. The hydraulic oil entering the oil ports respectively enters the P1 and P2 cavities. The flow passage Pf is communicated with the flow passage Pf on the cover plate 5. The valve body is provided with a spring chamber, in which a spring seat 13, a high-power spring 14 and a low-power spring 15 installed inside the high-power spring, a high-power spring adjusting seat 18, a low-power spring adjusting rod 16 are installed. It cooperates with the locking nut 7-2, the high-power spring locking nut 19 and the spring adjusting cover plate 21 to form a spring loading device.

[0058] The spring adjustment cover plate 21 is used to fix the large-power spring adjustment seat 18. The large-power spring adjustment seat 18 is used to install the large-power spring 14 and the small-power spring adjustment rod 16. By adjusting the large-power spring adjustment seat 18 (adjusting the compression amount of the large-power spring), the power curve can be changed (as Figure 9 shown) the first inflection point. After adjustment, it is locked with the large-power spring lock nut 19. The small-power spring adjustment rod 16 is used to install the small-power spring 15 and adjust the second inflection point of the power curve. After adjustment, it is locked with the lock nut 7-2. The spring seat 13 is used to transmit the acting force of the valve core to the spring.

[0059] The inner hole of the valve sleeve 2 has a structure with three different diameters d1, d2, and d3. The valve core 3 has a structure with three different diameters that matches the valve sleeve 2 and is installed inside the valve sleeve 2.

[0060] The two-position four-way reversing valve core 11 is provided with an axial hole a1 and a radial hole a2 for leading hydraulic oil to the small end of the two-position four-way reversing valve core 11. The two-position four-way reversing valve core 11 is provided with an O-ring groove for installing the O-ring 20-1. The large end face is connected to the reversing valve spring 10. The reversing valve spring 10 is installed on the spring seat 9. The other end of the spring seat 9 is connected to the reversing valve spring adjusting rod 8. The two-position four-way reversing valve is used to switch the flow state of the oil flowing into the pilot valve core 4. When the two-position four-way reversing valve core 11 is in the right position, the oil acts on two stepped surfaces of the pilot valve core 4. When it is in the left position, the oil acts on one stepped surface of the pilot valve core 4. The acting areas are different, and the acting forces on the valve core are different.

[0061] The pilot valve core 4 has a structure with two different diameters and is installed inside the cover plate 5. By adjusting the screwing depth of the reversing valve spring adjusting rod 8, the pre-tightening force of the reversing valve spring 10 is adjusted, controlling whether the two-position four-way reversing valve core changes direction and thus controlling the effective acting area of the pilot oil acting on the pilot valve core.

[0062] When the hydraulic oil at the pump outlet reaches the set value, the valve core 3 moves leftward under the acting force generated by the area difference and the acting force generated by the pilot valve core 4, overcoming the spring force of the large-power spring 14. The P1 chamber is connected to the A chamber, and the hydraulic oil flows to the variable piston chamber of the piston pump (as Figure 8 shown). The variable piston drives the swash plate to change the swing angle under the action of the hydraulic oil to realize the change of the pump output flow. While the variable piston moves, it rotates around the fulcrum pin 21 through the feedback rod 12, drives the valve sleeve 2 to move leftward through the feedback rod pin 17, and controls the opening size between the P1 chamber and the A chamber, so as to ensure that the product of the flow rate and the outlet pressure at the pump outlet is approximately constant.

[0063] The working principle is as follows:

[0064] The P, A, and T cavities on the valve body are respectively connected to the oil outlet of the plunger pump, the variable piston cavity of the plunger pump, and the oil return cavity. The feedback rod 12 is connected to the variable piston of the plunger pump. The hydraulic oil at the outlet of the pump enters the P1 and P2 cavities and acts on the annular end faces with an area difference formed by the valve core 3d1, d2, and d2d3. The pilot valve core 4 controls the oil to flow through the Pf flow channel and through the two-position four-way reversing valve core 11. Part of the oil is led to the small end face of the valve core through the a1 and a2 flow channels on the two-position four-way reversing valve core 11. The force received by the two-position four-way reversing valve core 11 is:

[0065] Pf*π*(d6^2) / 4=Kx.

[0066] Pf - Pilot oil

[0067] d6 - Diameter of the two-position four-way reversing valve core

[0068] K - Spring stiffness

[0069] x - Displacement of the two-position four-way reversing valve core

[0070] When it cannot overcome the spring force and move, part of the oil acts on the d4 and d5 step surfaces of the pilot valve core 4 through the Pf1 and Pf2 flow channels. At this time, the hydraulic pressure received by the valve core 3 is:

[0071] Pc*{π / 4*[(d1^2 - d2^2)+(d2^2 - d3^2)]}+Pf*π / 4*(d4^2 + d5^2);

[0072] Pc - Pump outlet pressure

[0073] Pf - Pilot oil

[0074] d1 - Valve core diameter one of valve core 3

[0075] d2 - Valve core diameter two of valve core 3

[0076] d3 - Valve core diameter three of valve core 3

[0077] d4 - Diameter of the pilot valve core 4

[0078] d5 - Diameter of the pilot valve core 4

[0079] When it overcomes the spring force and moves, part of the oil acts on the d5 step surface of the pilot valve core 4 through the Pf1 flow channel, and the oil on the d4 step surface flows back to the T port for pressure relief through the Pf2 flow channel. At this time, the hydraulic pressure received by the valve core 3 is:

[0080] Pc*{π / 4*[(d1^2 - d2^2)+(d2^2 - d3^2)]}+Pf*π / 4*d5^2;

[0081] Pc - Pump outlet pressure

[0082] Pf - Pilot oil

[0083] d1 - Spool 3 spool diameter one

[0084] d2 - Spool 3 spool diameter two

[0085] d3 - Spool 3 spool diameter three

[0086] d5 - Pilot spool 4 diameter

[0087] The calculated force on spool 3 is to match the spring force of the power spring. The force on spool 3 at each stage is determined by the spring force of the power spring with different sizes.

[0088] Working mode - The excavator is equipped with three modes: H (heavy load), S (standard), and L (ordinary). The operator selects the appropriate mode according to different operating conditions to make the engine output the most reasonable power.

[0089] In the H (S) mode, by adjusting the screwing depth of the reversing valve spring adjusting rod 8, the pre - tightening force of the reversing valve spring 10 is adjusted. So that the pilot spool 4 is not enough to overcome the spring force to move under the action of the control oil Pf. When the hydraulic oil at the pump outlet reaches the set value, spool 3 moves leftward under the action of the force generated by the area difference and the force generated by the pilot spool 4, overcoming the spring force of the large power spring 14. The P1 chamber is connected to the A chamber, and the hydraulic oil flows to the variable piston chamber of the piston pump. The variable piston pushes the swash plate to change the swing angle under the action of the hydraulic oil to realize the change of the pump output flow. While the variable piston moves, it rotates around the fulcrum pin 21 through the feedback rod 12, and drives the valve sleeve 2 to move leftward through the feedback rod pin 17 to control the opening size between the P1 chamber and the A chamber, so as to ensure that the product of the flow rate and the outlet pressure at the pump outlet is approximately constant, forming the first variable characteristic curve. By adjusting the d4 and d5 diameters of the pilot spool 4 for matching power, the actual power inflection point can be made to coincide with the theoretical power inflection point. When the pump outlet pressure rises to a certain value, the small power spring 15 also generates a force, and similarly, the second variable characteristic curve is formed.

[0090] In the L mode, the force exerted by the increasing control oil pressure Pf on the pilot spool 4 overcomes the spring force, causing it to move to the left. The oil acting on the d4 step surface of the pilot spool 4 flows back to the T port through the Pf2 passage and the two-position four-way directional control valve spool 11 for pressure relief, and a part of the control oil acts on the d5 step surface of the pilot spool 4. As the pump outlet pressure increases, the spool 3 moves under the action of the force generated by the area difference and the force generated by the pilot spool 4, achieving constant power control in this mode. Since the force-bearing area of the pilot spool 4 becomes smaller, the force acting on the spool 3 decreases accordingly. Thus, under the same pilot control oil condition, the pump outlet pressure corresponding to the first inflection point of constant power is higher than that of a single-stage spool and is closer to the inflection point corresponding to the theoretical power.

[0091] Currently, the secondary pressure output by a proportional valve is generally used as the pilot control oil. However, due to differences in the output characteristics of proportional valves from different manufacturers, it is difficult to match the power values in different modes that meet the requirements of the host factory with a single-stage pilot spool structure. The present invention adopts a stepped pilot spool structure. According to the secondary pressure output by the proportional valve, the cross-sectional diameter of the pilot spool 4 and the directional control valve spring 10 are adjusted and matched. By controlling whether the two-position four-way directional control valve spool 11 changes its direction, the effective acting area of the pilot spool is changed, thereby obtaining the power values in different modes.

[0092] In addition to the above embodiments, the present invention may have other implementation manners. For example, the two-position four-way directional control valve spool can be changed to other types of spool structures by modifying the flow passage, or the O-ring seal can be changed to a structure with a separate oil drain for the directional control valve spring chamber, or the pilot spool can be changed to a multi-stepped structure to achieve the same goal. Such solutions all fall within the protection scope required by the present invention.

[0093] Definitions of abbreviations and key terms:

[0094] Constant power - The product of the outlet pressure and the output flow rate of the piston pump is a set value (constant value), that is, the outlet pressure and flow rate of the pump satisfy a hyperbolic function relationship.

[0095] Directional control valve - A valve that uses the different relative positions of the spool and the valve body to achieve the connection, disconnection, or change of the liquid flow direction of each oil passage.

[0096] Control valve - Applied to a piston pump to control the displacement of the pump.

[0097] Power starting point - The inflection point at which the pump output flow rate automatically decreases as the pressure increases.

[0098] In addition, the terms "first" and "second" are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality of" means two or more unless specifically defined otherwise.

[0099] In the present invention, unless otherwise clearly specified and defined, the terms such as "mounted", "connected", "coupled", "fixed", etc. shall be construed broadly. For example, it may be a fixed connection, a detachable connection or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention may be understood according to specific circumstances.

[0100] In the present invention, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature may include the direct contact between the first and second features, or may include the situation where the first and second features are not in direct contact but in contact through additional features therebetween. Moreover, the first feature being "above", "over" and "on top of" the second feature includes that the first feature is directly above and obliquely above the second feature, or merely means that the horizontal height of the first feature is higher than that of the second feature. The first feature being "under", "beneath" and "underneath" the second feature includes that the first feature is directly below and obliquely below the second feature, or merely means that the horizontal height of the first feature is lower than that of the second feature.

[0101] In the description of this specification, the descriptions with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in a suitable manner in any one or more embodiments or examples.

[0102] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and purposes of the present invention.

Claims

1. A control valve for a constant power piston pump, characterized in that, It includes a valve body, a valve sleeve installed in the valve body, and a valve core nested and connected in the valve sleeve; One end of the valve core abuts against a pilot valve core, and the other end is provided with a spring loading device; The spring loading device can provide a spring force to the valve core for adjusting the power setting value of the piston pump; The pilot valve core is connected to the pressure oil output by the proportional valve through a two-position four-way directional control valve. By using different pressures output by the proportional valve, variable power control is achieved; the valve core cooperates with the valve sleeve. The valve core acts against the spring force of the spring loading device under the combined action of the outlet pressure oil and the pilot valve core, gradually opening the channel for the hydraulic oil to flow to the variable piston cavity of the piston pump, so that the variable piston pushes the swashplate of the piston pump under the action of the hydraulic oil; A feedback rod pin, a feedback rod, and a fulcrum pin are connected to the valve sleeve. One end of the feedback rod rotates around the fulcrum pin, and the other end is connected to the variable piston of the piston pump. When the variable piston moves, the feedback rod pin on the feedback rod drives the valve sleeve to move, gradually closing the channel for the hydraulic oil to flow to the variable piston cavity of the piston pump; When the hydraulic oil at the pump outlet reaches the set value, the valve core moves against the spring force of the spring loading device under the action force generated by the area difference and the action force generated by the pilot valve core. The channel for the hydraulic oil to flow to the variable piston cavity of the piston pump is connected, and the hydraulic oil flows to the variable piston cavity of the piston pump. The variable piston pushes the swashplate to change the swing angle under the action of the hydraulic oil to realize the change of the pump output flow. While the swashplate swings, it rotates around the fulcrum pin through the feedback rod, and drives the valve sleeve to move leftward through the feedback rod pin, controlling the opening size of the channel for the hydraulic oil to flow to the variable piston cavity of the piston pump, so as to ensure that the product of the flow rate and the outlet pressure at the pump outlet is approximately constant; The control valve for the constant power piston pump further includes a cover plate and an end cover; The pilot valve core is provided with a structure of two different diameters and is installed in the cover plate; By adjusting the screwing depth of the reversing valve spring adjusting rod, the pre-tightening force of the reversing valve spring is adjusted, and whether the two-position four-way directional control valve core reverses is controlled, thereby controlling the effective acting area of the pilot oil acting on the pilot valve core; The two-position four-way directional control valve is used to switch the flow state of the oil flowing into the pilot valve core. When the right position of the two-position four-way directional control valve core works, the oil acts on two step surfaces of the pilot valve core. When the left position works, the oil acts on one step surface of the pilot valve core.

2. The control valve for a constant power piston pump according to claim 1, characterized in that, The two-position four-way directional control valve includes a reversing valve spring adjusting rod, a reversing valve spring seat, a reversing valve spring, and a two-position four-way directional control valve core; the two-position four-way directional control valve is used to switch the flow state of the oil flowing into the pilot valve core. When the right position of the two-position four-way directional control valve core works, the oil acts on two step surfaces of the pilot valve core. When the left position works, the oil acts on one step surface of the pilot valve core; The two-position four-way directional control valve core is installed in the cover plate. The two-position four-way directional control valve core is provided with an axial hole and a radial hole for leading the hydraulic oil to the small end of the two-position four-way directional control valve core; The large end face of the two-position four-way directional control valve core is connected to the reversing valve spring; the reversing valve spring is installed on the spring seat, the other end of the spring seat is connected to the reversing valve spring adjusting rod, the reversing valve spring adjusting rod is installed on the end cover with a threaded hole and fixed by a locking nut, and the end cover is installed on the cover plate.

3. The control valve for a constant power plunger pump according to claim 2, characterized in that, The two-position four-way reversing valve spool is provided with an O-ring groove for installing an O-ring to prevent hydraulic oil from entering the spring chamber.

4. The control valve for a constant power piston pump according to claim 2, characterized in that, The pilot valve spool is provided with a structure of two different diameters and is installed in the cover plate. The pre-tightening force of the reversing valve spring is adjusted by adjusting the screwing depth of the reversing valve spring adjusting rod, so as to control whether the two-position four-way reversing valve spool reverses, and further control the effective acting area of the pilot oil acting on the pilot valve spool.

5. The control valve for a constant power piston pump according to claim 1, characterized in that, The spring loading device includes a spring seat, a large-power spring, a small-power spring, a large-power spring adjusting seat, a small-power spring adjusting rod, a locking nut, a large-power spring locking nut, and a spring adjusting cover plate; The valve body is provided with a spring chamber, in which a spring seat, a large-power spring, a small-power spring installed in the large-power spring, a large-power spring adjusting seat, and a small-power spring adjusting rod are installed; The spring adjusting cover plate is used to fix the large-power spring adjusting seat. The large spring adjusting seat is used to install the large-power spring and the small-power spring adjusting rod. By adjusting the large-power spring adjusting seat, the first inflection point of the power curve is changed. After adjustment, it is locked with the large-power spring locking nut. The small-power spring adjusting rod is used to install the small-power spring and adjust the second inflection point of the power curve. After adjustment, it is locked with the locking nut. The spring seat is used to transmit the acting force of the spool to the spring.

6. The control valve for a constant power piston pump according to claim 1, wherein The inner hole of the valve sleeve is provided with a structure of different diameters. The spool is provided with a structure of different diameters that matches the valve sleeve and is installed in the valve sleeve.

7. The control valve for a constant power plunger pump according to claim 6, characterized in that, The inner hole of the valve sleeve is provided with three sections of different diameters d1, d2, and d3. The spool is provided with three sections of different diameters that match the valve sleeve and is installed in the valve sleeve.

8. The control valve for a constant power piston pump according to claim 1, characterized in that, The valve body is provided with oil ports and flow channels; The valve sleeve is installed in the valve body to form a P1 chamber, a P2 chamber, an A chamber, and a T chamber; The P2 chamber is used to introduce the pump outlet pressure, so as to act on the spool with the annular areas of d2 and d3. The T chamber is used for pressure relief; the P1 chamber is used to introduce the pump outlet pressure, so as to act on the spool with the annular areas of d1 and d2; the movement of the spool will cause the A chamber to communicate with the variable piston chamber.

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