Design method for solving problem of advanced cutting-off of plunger pump

Abstract

The invention discloses a design method for solving advanced cutting-off of a plunger pump. The problem that an existing plunger pump cuts off variables in advance under the conditions of large displacement and high pressure is solved. By adjusting the four parameters of delta hmax, K, PSP and delta, the following three conditions are met at the same time: (1) MA + MDgt; 0, (2) when the plunger pump is at the maximum displacement, Pfmaxt; (3) the plunger pump is within the rated pressure, MAL; the delta hmax is the compression amount of the pressure regulating spring when the plunger pump is in the maximum displacement, the K is the rigidity of the pressure regulating spring, the PSP is an oil supplementing pressure set value, the Pfmax is the hydraulic thrust required when the plunger pump is in the maximum displacement, the delta is the deflection angle of the valve plate, clockwise deflection is defined as positive, anticlockwise deflection is defined as negative, and the delta is the deflection angle of the valve plate. MA is the pressure unbalance moment of the plunger to the swash plate, MD is the load moment of the variable mechanism, and MK is the acting moment of the pressure adjusting spring to the swash plate. The swash plate type plunger pump has the beneficial effects that by means of the design, the swash plate type plunger pump has the advantages of being high in response speed and accurate in cut-off pressure set value control.

Description

Technical Field

[0001] The invention relates to the field of inclined plate type plunger pumps, and in particular to a design method for solving the problem of premature cutting off of a plunger pump. Background Art

[0002] With the diversification of agricultural machinery, China's agricultural machinery varieties continue to enrich, including tractors, combine harvesters, conveyors, seeders, sprayers and other mechanical equipment. The continuous updating and improvement of these mechanical equipment have improved the efficiency and quality of farmland operations. At the same time, customers' requirements for various agricultural machinery are constantly increasing, especially in the field of harvesters, and the reliability requirements for the hydraulic system of the whole machine are very high. As the core power system in the hydraulic system, the performance of the plunger pump directly affects the overall operation quality of the host. At present, in the process of matching with the host system, the main phenomena are the host's inability to harvest and the host's lack of power for heavy-load climbing. At the same time, it was determined that the premature cutting off of the variable of the inclined plate in the plunger pump under high pressure is the main reason for the lack of power for heavy-load climbing of the host. Summary of the invention

[0003] In order to solve the problem of the prior art plunger pump cutting off the variable in advance at a large displacement and high pressure, the present invention provides a design method for solving the problem of the plunger pump cutting off in advance.

[0004] The technical solution of the present invention is: a design method for solving the problem of premature cutting of a plunger pump, by adjusting Δh max , K, P SP , δ, these four parameters make the following three conditions meet at the same time: ①M A +M D >0,②When the plunger pump is at maximum displacement, P fmax <P SP , ③ The plunger pump is within the rated pressure, M A <M k , the Δh max is the compression amount of the pressure regulating spring when the plunger pump has the maximum displacement, K is the stiffness of the pressure regulating spring, and P is SP is the charge pressure setting value, the P fmax is the hydraulic thrust required when the plunger pump is variable to the maximum displacement, the δ is the deflection angle of the valve plate, and the clockwise deflection is defined as positive and the counterclockwise deflection is defined as negative. A is the pressure unbalance torque of the plunger on the swash plate, and the M D is the variable mechanism load moment, the M K is the torque of the pressure regulating spring on the swash plate.

[0005] As a further improvement of the present invention, during the operation of the plunger pump, the swash plate is mainly subjected to the following forces: the pushing force F1 of the sliding shoe on the swash plate, the supporting force F2, F2' of the bearing on the swash plate, the spring force F3 of the central preload device, the load thrust F4 of the variable mechanism on the swash plate, the rotational inertia force F5 when the swash plate and the return plate rotate around the x-axis, the inertia force F6 of the plunger assembly when the swash plate changes the inclination angle β, and the friction force F7 between the sliding shoe and the swash plate when the sliding shoe deflects (the sliding support of the swash plate of this type of plunger pump is a crescent roller bearing, and its sliding friction force can be ignored). These forces will generate a torque that can increase or decrease the inclination angle of the swash plate. The present invention mainly studies the pressure imbalance torque M of the plunger on the swash plate generated by the pushing force F1 and the load thrust F4. A and variable mechanism load moment M D The influence of changing the inclination angle of the swash plate, where the pressure unbalance torque M of the plunger on the swash plate A The average moment M of the plunger on the swash plate including the valve plate envelope area a The average moment of pressure imbalance between the piston and the swash plate in the transition zone is M b ; The above torque definition is that the torque that increases the inclination angle of the swash plate is "+", and the torque that decreases the inclination angle of the swash plate is "-".

[0006] As a further improvement of the present invention, the pressure unbalanced moment M of the plunger on the swash plate A The adjustment equation is: A =M a +M b ; where M a M is the average moment of the plunger on the swash plate in the envelope area of ​​the valve plate, a =M a1 +M a2 , the M a1 is the average moment of the envelope area on the swash plate rotating shaft, the M a2 is the average moment of the envelope area under the swash plate rotation axis, then:

[0007]

[0008]

[0009] Where:

[0010] A—— plunger cross-sectional area, R——cylinder distribution circle radius; P s ——Pump oil outlet pressure; P o ——pressure at the pump suction port; δ——deflection angle of the valve plate; β——maximum inclination angle of the swash plate; ψ1, ψ1′——dead angle of the transition zone on the rotating shaft of the swash plate; ψ2, ψ2′——dead angle of the transition zone below the rotating shaft of the swash plate;

[0011] ψa1 ——The cylinder body’s turning angle in the oil discharge envelope,

[0012] ψ a1 ′——The turning angle of the cylinder body in the upper envelope area of ​​the oil suction side,

[0013] ψ a2 ——The cylinder body’s turning angle in the oil discharge envelope,

[0014] ψ a2 ′——The turning angle of the cylinder body in the lower envelope area of ​​the oil suction test, Where λ = 0, 1, 2, ...;

[0015] j, k, l, r——are constants, Round up any decimal number, such as j=80.2, then j is 81.

[0016] As a further improvement of the present invention, wherein M b is the average unbalanced moment of pressure on the swash plate from the plunger in the transition hydraulic zone (upper and lower zones), M b =M b1 +M b2 , the M b1 is the average unbalanced pressure moment of the plunger on the swash plate in the transition hydraulic zone on the swash plate rotating shaft. b2 is the average unbalanced pressure moment of the piston on the swash plate in the transition hydraulic zone under the swash plate rotating axis, then: when ψ1′-δ<ψ u <ψ1+δorψ2-δ<ψ d <ψ2′+δ,

[0017]

[0018] Where:

[0019] P u ——Average pressure of the plunger cavity in the transition hydraulic zone on the swash plate;

[0020] P d ——Average pressure of the plunger cavity in the transition hydraulic zone under the swash plate;

[0021] ψ u ——rotation angle of the cylinder in the upper transition hydraulic zone; ψ u =ψ′1-δ-λ……0°……ψ1+δ-λ;

[0022] ψ d ——the turning angle of the cylinder in the lower transition hydraulic zone; ψ d=ψ2-δ-λ……0°……ψ2′+δ-λ, where λ=0, 1, 2, 3……;

[0023] m, n are constants, m = ψ1+ψ1′+3, n = ψ2+ψ2′+3, ψ1, ψ′1, ψ2, ψ2′ are rounded toward zero; for example, ψ1 = 9.8°, ψ1′ = 8.5°, then m = 9+8+3 = 20.

[0024] Arranged:

[0025]

[0026] As a further improvement of the present invention, the load moment M of the variable mechanism on the swash plate D The adjustment equation is: D =M k +M P , the M k is the torque of the pressure regulating spring on the swash plate, and the M P is the torque of the hydraulic thrust of the piston on the swash plate; where:

[0027] Where: M k =-2Δh max KL1

[0028]

[0029] Where:

[0030] D——variable piston diameter;

[0031] P k ——Hydraulic thrust acting on the variable piston, P kmax =P SP ;

[0032] Δh max ——Compression amount of pressure regulating spring (when the plunger pump is at maximum displacement);

[0033] K——pressure regulating spring stiffness.

[0034] As a further improvement of the present invention, by defining M A and M D The value range can flexibly control the magnitude and direction of the swash plate torque. A +M D >0, the torque increases the inclination angle of the swash plate, which can increase the upper limit of the pressure cut-off setting value, but there are risks such as slow response speed of the plunger pump and failure of pressure cut-off. A +M D<0, the torque reduces the inclination angle of the swash plate, which can effectively improve the response speed of the plunger pump, but at the same time it is accompanied by the risk of premature cut-off of the pressure cut-off point and low volumetric efficiency. A +M D value, improve the various extreme working conditions of the plunger pump, and meet the matching of the plunger pump with different host working conditions.

[0035] As a further improvement of the present invention, the adjustment equation of the hydraulic thrust required when the plunger pump is variable to the maximum displacement needs to satisfy: P fmax <P SP ;

[0036] in:

[0037]

[0038] The beneficial effect of the present invention is that, through the design of the present invention, the scientificity of the design and the functionality of the product are improved, so that the swash plate plunger pump has the advantages of fast response speed and precise control of the cut-off pressure setting value. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram of the structure of the present invention.

[0040] Figure 2 Force analysis diagram of variable mechanism.

[0041] Figure 3 Swash plate lever arm analysis diagram.

[0042] Figure 4 Schematic diagram of the distribution plate structure

[0043] Figure 5 Relationship diagram between cylinder rotation angle and swash plate lever arm.

[0044] Figure 6 Trend diagram of cylinder angle and plunger chamber pressure.

[0045] Figure 7 Schematic diagram of the principle of the present invention.

[0046] Figure 8 This is a test data diagram for adjusting parameters of the present invention.

[0047] In the figure, 1. housing; 2. return plate; 3. cylinder block; 4. distribution plate; 5. rear cover; 6. oil charge pump; 7. rotating shaft; 8. ball joint; 9. inclined plate; 10. sliding shoe; 11. plunger; 12. spring. DETAILED DESCRIPTION

[0048] The embodiments of the present invention are further described below in conjunction with the accompanying drawings:

[0049] Depend on Figure 1 Combination Figure 2-8 As shown, a design method for solving the problem of premature cutting off of a plunger pump, the plunger pump generally includes a housing 1, a return plate 2, a cylinder body 3, a distribution plate 4, a rear cover 5, an oil replenishment pump 6, a rotating shaft 7, a ball joint 8, a swash plate 9, a slipper 10, a plunger 11, and a spring 12.

[0050] Adjust Δh according to the following equation max , K, P SP , δ, the following three conditions are satisfied at the same time:

[0051] ①M A +M D >0,②When the plunger pump is at maximum displacement, P fmax <P SP , ③ The plunger pump is within the rated pressure, M A <M k The Δh max is the compression amount of the pressure regulating spring when the plunger pump has the maximum displacement, K is the stiffness of the pressure regulating spring, and P is SP is the charge pressure setting value, the P fmax is the hydraulic thrust required when the plunger pump is variable to the maximum displacement, δ is the deflection angle of the valve plate, and M A is the pressure unbalance torque of the plunger on the swash plate, and the M D is the variable mechanism load torque, the M K is the torque of the pressure regulating spring on the swash plate.

[0052] Piston pump swash plate torque adjustment equation: M A +M D >0

[0053] Among them, M A =M a +M b ;

[0054] M a =M a1 +M a2 , the M a1 is the average moment of the envelope area on the swash plate rotating shaft, the M a2 is the average moment of the envelope area under the swash plate rotation axis, then:

[0055]

[0056]

[0057] Where:

[0058] A—— plunger cross-sectional area, R——cylinder distribution circle radius; P s——Pump oil outlet pressure; P o ——pressure at the pump suction port; δ——deflection angle of the valve plate; β——maximum inclination angle of the swash plate; ψ1, ψ1′——dead angle of the transition zone on the rotating shaft of the swash plate; ψ2, ψ2′——dead angle of the transition zone below the rotating shaft of the swash plate;

[0059] ψ a1 ——The cylinder body’s turning angle in the oil discharge envelope,

[0060] ψ a1 ′——The turning angle of the cylinder body in the upper envelope area of ​​the oil suction side,

[0061] ψ a2 ——The cylinder body’s turning angle in the oil discharge envelope,

[0062] ψ a2 ′——The turning angle of the cylinder body in the lower envelope area of ​​the oil suction test, Among them, λ=0, 1, 2...; j, k, l, r——are constants, Round up any decimal number, such as j=80.2, then j is 81.

[0063] M b is the average moment of pressure imbalance between the piston and the swash plate in the transition hydraulic zone, M b =M b1 +M b2 , the M b1 is the average unbalanced pressure moment of the plunger on the swash plate in the transition hydraulic zone on the swash plate rotating shaft. b2 is the average unbalanced pressure moment of the piston on the swash plate in the transition hydraulic zone under the swash plate rotating axis, then: when ψ1′-δ<ψ u <ψ1+δorψ2-δ<ψ d <ψ2′+δ,

[0064]

[0065] Where:

[0066] P u ——Average pressure of the plunger cavity in the transition hydraulic zone on the swash plate;

[0067] P d ——Average pressure of the plunger cavity in the transition hydraulic zone under the swash plate;

[0068] ψ u ——rotation angle of the cylinder in the upper transition hydraulic zone; ψ u =ψ′1-δ-λ……0°……ψ1+δ-λ;

[0069] ψd ——the turning angle of the cylinder in the lower transition hydraulic zone; ψ d =ψ2-δ-λ……0°……ψ2′+δ-λ, where λ=0, 1, 2, 3……;

[0070] m, n are constants, m = ψ1+ψ1′+3, n = ψ2+ψ2′+3, ψ1, ψ′1, ψ2, ψ2′ are rounded toward zero; for example, ψ1 = 9.8°, ψ1′ = 8.5°, then m = 9+8+3 = 20.

[0071] Arranged:

[0072]

[0073] Load moment M of variable mechanism on swash plate D The adjustment equation is: D =M k +M P , the M k is the torque of the pressure regulating spring on the swash plate, and the M P is the torque of the hydraulic thrust of the piston on the swash plate; where:

[0074] M k =-2Δh max KL1

[0075]

[0076] Where:

[0077] D——variable piston diameter;

[0078] P k ——Hydraulic thrust acting on the variable piston, P kmax =P SP ;

[0079] Δh max ——Compression amount of pressure regulating spring (when the plunger pump is at maximum displacement);

[0080] K——pressure regulating spring stiffness.

[0081] The hydraulic thrust P required when the piston pump changes to the maximum displacement fmax Less than the charge pressure setting value P SP :P fmax <P SP ,in

[0082] When the piston pump is within the rated pressure, the pressure unbalance moment M of the piston on the swash plate A Less than the torque M of the pressure regulating spring on the swash plate K ;

[0083] Among them, M k =-2Δh max KL1

[0084] The following table is based on the above design method, and the max , K, P SP See the attached three sets of test data for adjusting the four parameters of Figure 8 .

[0085] The working principle of the present invention is as follows: Figure 2 The figure shows the force analysis of the swash plate in the plunger pump of the present invention. During operation, the swash plate is mainly subjected to the following forces: the pushing force F1 of the sliding shoe on the swash plate, the supporting force F2, F2' of the bearing on the swash plate, the spring force F3 of the center preload device, the load thrust F4 of the variable mechanism on the swash plate, the rotational inertia force F5 when the swash plate and the return plate rotate around the x-axis, the inertia force F6 of the plunger assembly when the swash plate changes the inclination angle β, and the friction force F7 between the sliding shoe and the swash plate when the sliding shoe deflects (the sliding support of the swash plate of this type of plunger pump is a crescent roller bearing, and its sliding friction force can be ignored). These forces will generate a torque that can increase or decrease the inclination angle of the swash plate. The present invention mainly studies the pressure imbalance torque M of the plunger on the swash plate generated by the pushing force F1 and the load thrust F4. A and variable mechanism load moment M D The influence of changing the inclination angle of the swash plate, where the pressure unbalance torque M of the plunger on the swash plate A The average moment M of the plunger on the swash plate including the valve plate envelope area a The average moment of pressure imbalance between the piston and the swash plate in the transition zone is M b .

[0086] like Figure 4 As shown, the distribution plate of the present invention is provided with two triangular damping grooves in the upper and lower transition areas. When the plunger cylinder window transitions from the oil suction side to the oil discharge side, the plunger cavity pressure changes from P o Rise to P s When the pressure in the plunger cavity changes from P to s Down to P o During the operation of the plunger pump, it can effectively play the role of pre-pressurization and pre-pressure relief, alleviate flow and pressure pulsation, and reduce noise, cavitation and other phenomena caused by sudden changes in high and low pressure.

[0087] According to the formula <3> It can be seen that the average moment M in the envelope area is a The value is related to the plunger cavity pressure P and the force arm A′B′. In the envelope area, P is a constant value P o or P s The force arm A′B′ generated by the plunger on the swash plate is the vertical distance from any point on the motion trajectory of the sliding shoe in the swash plate plane to the swash plate rotation axis (e.g. Figure 3 As shown), a periodic change is formed in the upper and lower halves of the slant disk (as shown Figure 5 The distribution form of the force arm A'B' in the envelope area is related to the structural parameters of the flow distribution mechanism. The flow distribution structure of the present invention is shown in Figure 4, where the dead angle ψ1 = ψ2', ψ2 = ψ1', and the clockwise deflection is defined as positive and the counterclockwise deflection is defined as negative. When the flow distribution plate deflects clockwise, ψ1>ψ2, and the average moment M of the plunger in the envelope area on the inclined plate a <0, this torque will make the swash plate return to the neutral position, that is, the position of β = 0. On the contrary, when the valve plate deflects counterclockwise, ψ1<ψ2, then M a >0, the torque will cause the swash plate to move to a larger inclination angle.

[0088] According to the formula <5> It can be seen that the present invention can adjust the size of the dead angle of the transition area of ​​the distribution plate to achieve the pressure P u and P d The increase and decrease of M b The size and direction of the value can be precisely adjusted. According to the structure parameters of the distribution plate described in the present invention, the size of the dead angle of the transition zone can be precisely controlled by adjusting the deflection angle δ. Specifically, Figure 6 As shown in the figure, when the valve plate deflects clockwise by an angle δ, ψ1 and ψ2′ will increase, while ψ2 and ψ2′ will decrease accordingly. This change will directly lead to P u The value increases, P d The piston exerts an unbalanced pressure on the swash plate in the transition zone. b Conversely, when the valve plate deflects counterclockwise δ, the average pressure unbalanced moment M of the plunger on the inclined plate in the transition zone is b Reduce.

[0089] According to the formula <6> It can be seen that the present invention can adjust the pressure regulating spring stiffness K, the maximum compression amount Δh of the pressure regulating spring max , and the charge pressure setting value P SP To change M D The value of M D is the load torque of the variable mechanism, which is the key torque to increase the inclination angle of the swash plate. max , or reduce the charge pressure setting value P SP When the inclination angle of the swash plate increases, the moment M D The main advantage of this adjustment is that it improves the response speed of the plunger pump back to the center (or initial position) because the swash plate can be pushed back to a smaller inclination angle more easily. However, this adjustment also has risks, especially when the stiffness K of the pressure regulating spring and the maximum compression Δh max The set overpressure or charge pressure setting value PSP If it is too small, the hydraulic thrust P required for the plunger pump to reach its maximum displacement will be fmax Greater than the charge pressure setting value P SP . This limits its ability to reach the maximum displacement. On the contrary, if the pressure regulating spring stiffness K and the maximum compression Δh are reduced max , or increase the charge pressure setting value P SP , then the moment M that pushes the swash plate to increase its inclination angle D This adjustment is beneficial to ensure the stability of the plunger pump under high displacement and high pressure conditions, because it reduces the risk of the swash plate returning to zero under high pressure. However, this adjustment may have another problem: when the system needs to cut off the pressure to protect the pump or other components, if the stiffness K of the pressure regulating spring and the maximum compression Δh max The setting value P of the oil filling pressure is too small or SP If it is too large, then when the pressure is cut off, the torque M acting on the swash plate by the pressure regulating spring K It may be smaller than the pressure unbalance torque M of the plunger pump on the swash plate A . Causes the variable piston to A >M K In the event of a failure, the pressure cut-off may fail to return to the neutral position.

[0090] In the description of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0091] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. In addition, in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0092] Technical personnel should note that although the present invention has been described according to the above specific implementation methods, the inventive concept of the present invention is not limited to this invention, and any modification using the inventive concept will be included in the scope of protection of the patent right of the present invention.

Claims

1. A design method for solving the problem of premature cutting off of a plunger pump, characterized in that : By adjusting Δh max , K, P SP , δ, these four parameters make the following three conditions meet at the same time: ①M A +M D >0,②When the plunger pump is at maximum displacement, P fmax <P SP , ③ The plunger pump is within the rated pressure, M A <M k , the Δh max is the compression amount of the pressure regulating spring when the plunger pump has the maximum displacement, K is the stiffness of the pressure regulating spring, and P is SP is the charge pressure setting value, the P fmax is the hydraulic thrust required when the plunger pump is variable to the maximum displacement, the δ is the deflection angle of the valve plate, and the clockwise deflection is defined as positive and the counterclockwise deflection is defined as negative. A is the pressure unbalance torque of the plunger on the swash plate, and the M D is the variable mechanism load moment, the M K is the torque of the pressure regulating spring on the swash plate.

2. A design method for solving the problem of premature cutting off of a plunger pump according to claim 1, characterized in that The pressure unbalanced moment M of the plunger on the swash plate A and variable mechanism load moment M D The influence of changing the inclination angle of the swash plate, where the pressure unbalance torque M of the plunger on the swash plate A The average moment M of the plunger on the swash plate including the valve plate envelope area a The average moment of pressure imbalance between the piston and the swash plate in the transition zone is M b ; The above torque definition indicates that the torque that increases the inclination angle of the swash plate is "+", and the torque that decreases the inclination angle of the swash plate is "-".

3. A design method for solving the problem of premature cutting off of a plunger pump according to claim 1, characterized in that The pressure unbalanced moment M of the plunger on the swash plate A The adjustment equation is: A =M a +M b ; where M a M is the average moment of the plunger on the swash plate in the envelope area of ​​the valve plate, a =M a1 +M a2 , the M a1 is the average moment of the envelope area on the swash plate rotating shaft, the M a2 is the average moment of the envelope area under the swash plate rotation axis, then: Where: A—— plunger cross-sectional area, R——cylinder distribution circle radius; P s ——Pump oil outlet pressure; P o ——pressure at the pump suction port; δ——deflection angle of the valve plate; β——maximum inclination angle of the swash plate; ψ1, ψ1′——the dead angle of the transition zone on the rotating shaft of the swash plate; ψ2, ψ2′——the dead angle of the transition zone below the rotating shaft of the swash plate; ψ a1 ——The cylinder body’s turning angle in the oil discharge envelope, ψ a1 ′——The turning angle of the cylinder body in the upper envelope area of ​​the oil suction side, ψ a2 ——The cylinder body’s turning angle in the oil discharge envelope, ψ a2 ′——The turning angle of the cylinder body in the lower envelope area of ​​the oil suction test, Among them, λ=0, 1, 2...; j, k, l, r——are constants, Any decimal number is rounded up.

4. A design method for solving the problem of premature cutting off of a plunger pump according to claim 3, characterized in that in, M b is the average moment of pressure imbalance between the piston and the swash plate in the transition hydraulic zone, M b =M b1 +M b2 , the M b1 is the average unbalanced pressure moment of the plunger on the swash plate in the transition hydraulic zone on the swash plate rotating shaft. b2 is the average unbalanced pressure moment of the piston on the swash plate in the transition hydraulic zone under the swash plate rotating axis, then: when ψ1′-δ<ψ u <ψ1+δorψ2-δ<ψ d <ψ2′+δ, Where: P u ——Average pressure of the plunger cavity in the transition hydraulic zone on the swash plate; P d ——Average pressure of the plunger cavity in the transition hydraulic zone under the swash plate; ψ u ——The turning angle of the cylinder in the upper transition hydraulic zone; ψ u =ψ′1-δ-λ……0°……ψ1+δ-θ; ψ d ——The turning angle of the cylinder in the lower transition hydraulic zone; ψ d =ψ2-δ-λ……0°……ψ2′+δ-θ, where θ=0, 1, 2, 3……; m, n——constants, m=ψ1+ψ1′+3, n=ψ2+ψ2′+3, ψ1, ψ11, ψ2, ψ2′ are rounded to zero; Arranged:

5. A design method for solving the problem of premature cutting off of a plunger pump according to claim 1, characterized in that Load moment M of variable mechanism on swash plate s The adjustment equation is: s =M k +M P , the M k is the torque of the pressure regulating spring on the swash plate, and the M P is the torque of the hydraulic thrust of the piston on the swash plate; where: M k =-2Δh max KL1 Where: D——variable piston diameter; P k ——Hydraulic thrust acting on the variable piston, P kmax =P SP ; Δh max ——Compression amount of pressure regulating spring (when the plunger pump is at maximum displacement); K——pressure regulating spring stiffness.

6. A design method for solving the problem of premature cutting off of a plunger pump according to claim 1, characterized in that By limiting M A and M D The value range can flexibly control the magnitude and direction of the swash plate torque. A +M D >0, the torque increases the inclination angle of the swash plate, which can increase the upper limit of the pressure cut-off setting value, but there are risks such as slow response speed of the plunger pump and failure of pressure cut-off. A +M D <0, the torque reduces the inclination angle of the swash plate, which can effectively improve the response speed of the plunger pump, but at the same time it is accompanied by the risk of premature cut-off of the pressure cut-off point and low volumetric efficiency. A +M D value, improve the various extreme working conditions of the plunger pump, and meet the matching of the plunger pump with different host working conditions.

7. A design method for solving the problem of premature cutting off of a plunger pump according to claim 1, characterized in that The adjustment equation for the hydraulic thrust required when the piston pump is variable to the maximum displacement must satisfy: P fmax <P SP ; in:

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