A high-pressure axial plunger pump sliding shoe friction torque measuring device and method

Abstract

This invention discloses a device and method for measuring the frictional torque of a high-pressure axial piston pump slipper, belonging to the technical field of axial piston pumps. The device uses a swashplate as the friction transmission component, connecting the back of the swashplate to an elastic sensitive element. Through strain gauges arranged on an elastic beam and a Wheatstone bridge circuit, the tangential bending strain signal caused by the slipper frictional torque is acquired. Combined with hydraulic loading, speed detection, and high-speed signal acquisition, synchronous measurement of friction signals under different operating conditions is achieved. During measurement, the system is first zeroed and statically calibrated in situ to obtain the calibration coefficient between the frictional torque and the output voltage. Then, the pump body is started and the load pressure is adjusted. The full-bridge output voltage, pressure, and speed signals are acquired, and the slipper frictional torque is calculated based on the calibration relationship. This invention enables direct, real-time measurement of frictional torque and effectively suppresses interference from axial loads and overturning moments, improving measurement accuracy and reliability.

Description

Technical Field

[0001] This invention relates to the field of axial piston pump technology, and more specifically to a device and method for measuring the friction torque of a high-pressure axial piston pump slipper. Background Technology

[0002] Axial piston pumps are widely used in aerospace, high-end hydraulic equipment, and construction machinery. As one of the key friction pairs within the pump, the slipper operates under high pressure, high speed, and complex load conditions for extended periods. Its friction and lubrication condition directly affects the pump's efficiency, reliability, and service life.

[0003] Because the slipper is located inside the pump body, installation space is limited, and the working environment is complex, conventional sensors are difficult to place directly in the friction contact area between the slipper and the swashplate. Adding measuring elements near the friction interface may alter the original oil film lubrication and stress state, leading to distorted measurement results. Therefore, existing methods mostly estimate slipper friction indirectly through overall pump power loss, efficiency changes, or empirical models, making it difficult to directly obtain instantaneous frictional force or torque.

[0004] The true frictional torque of a slipper is influenced by factors such as hydraulic load, motion speed, oil film state, attitude changes, and local contact state. Existing simplified test benches can typically only simulate a single load or a single motion pattern, making it difficult to reproduce the complex motions and load changes under actual working conditions. Furthermore, if factors such as axial load, overturning moment, installation errors, and structural deformation directly affect the measurement structure or sensor output, the measured signal will be mixed with non-frictional torque components, making it difficult to accurately reflect the true frictional torque of the slipper interface.

[0005] Therefore, it is necessary to propose a testing device and method that can directly measure the friction torque of a slipper under high pressure loading and rotational conditions, so as to improve the accuracy and stability of friction torque testing. Summary of the Invention

[0006] The purpose of this invention is to provide a device and method for measuring the friction torque of a high-pressure axial piston pump slipper, so as to solve the problems existing in the prior art.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: Firstly, the present invention proposes a high-pressure axial piston pump slipper friction torque measuring device, comprising:

[0008] The testing unit includes a motor, a cylinder, a swashplate, an elastic sensing element, and a housing. The motor is connected to the cylinder's main shaft, driving the cylinder to rotate. Multiple plungers are circumferentially arranged within the cylinder, each plunger's head connected to a sliding shoe. An oil film is formed between the sliding shoe and the swashplate's working surface, allowing the sliding shoe to slide along the swashplate's working surface under the support of the oil film. The elastic sensing element includes an outer hub and an inner hub, concentrically arranged. The inner hub is fixedly connected to the back of the swashplate from its front end, and the outer hub is fixedly connected to the housing from its rear end. Multiple radially extending elastic beams are provided between the outer and inner hubs, each elastic beam equipped with a strain gauge for detecting tangential bending strain. The strain gauges form a Wheatstone bridge, superimposing and outputting the strain signals caused by frictional torque.

[0009] The signal acquisition and processing unit includes a speed sensor, a signal acquisition card, and a host computer. The speed sensor is installed on the motor shaft. Both the speed sensor and the strain gauge are electrically connected to the signal acquisition card. The signal acquisition card is used at least to acquire the motor speed and strain gauge signals and upload them to the host computer for processing.

[0010] As a further improvement of the present invention, a hydraulic loading unit is also included. The hydraulic loading unit includes a pressure sensor and a relief valve. One end of the relief valve is connected to the piston outlet oil circuit, and the other end is connected to the oil tank. The pressure sensor is set in the loading oil circuit between the piston cavity oil port and the relief valve inlet to monitor the discharge pressure. By adjusting the relief valve overflow pressure, the load of the piston under different working conditions can be simulated.

[0011] As a further improvement of the present invention, the central axis direction of the elastic sensitive element is taken as the Z-axis, the radial extension direction of the elastic beam between the inner hub and the outer hub is taken as the beam length direction, and the cross section of the elastic beam perpendicular to the beam length direction is rectangular, with the side length of the rectangular cross section along the Z-axis direction being greater than the side length perpendicular to the beam length direction.

[0012] As a further improvement of the present invention, the number of elastic beams is four, forming a cross-shaped structure between the outer hub and the inner hub.

[0013] Secondly, the present invention also proposes a method for measuring the frictional torque of a high-pressure axial piston pump slipper, using the aforementioned high-pressure axial piston pump slipper frictional torque measuring device. The method includes the following steps:

[0014] Step S1, Installation and Zeroing: Rigidly connect the back of the swashplate to the inner hub of the elastic sensing element, and fix the outer hub of the elastic sensing element to the housing, so that the swashplate forms an elastic connection support through the elastic sensing element; connect each strain gauge to the Wheatstone full-bridge circuit and connect the signal acquisition card; perform zero-point adjustment after the system is powered on and preheated.

[0015] Step S2, Strain Gauge Full Bridge Assembly and Decoupling Settings: A pair of strain gauges distributed along the first radial direction on opposite elastic beams form a first Wheatstone full bridge, and a pair of strain gauges distributed along the second radial direction orthogonal to the first radial direction on opposite elastic beams form a second Wheatstone full bridge; the strain gauges on the tension side and the compression side of the elastic beams under tangential bending are respectively connected to the corresponding bridge arms of the full bridge circuit, so that the tangential bending strain caused by the frictional torque forms a differential superposition in the full bridge output, and the unidirectional strain caused by the axial load and the symmetrical strain caused by the overturning moment cancel each other out in the full bridge output;

[0016] Step S3, In-situ Static Calibration: Lock the pump spindle, install a standard lever arm at a position coaxial with the swashplate, apply standard loads step by step along the tangential direction to generate multiple known standard friction torque values, record the friction torque channel calibration output voltage after zero-point subtraction, polarity unification superposition and signal amplification processing of the corresponding full-bridge output voltage, and obtain the friction torque-voltage calibration coefficient K by fitting;

[0017] Step S4, Friction Torque-Strain Conversion: Start the motor and drive the cylinder to rotate, so that the head of the plunger drives the slipper to slide on the surface of the swashplate; the friction force generated by the slipper acts on the swashplate and forms a friction torque, which is transmitted through the swashplate to the inner hub of the elastic sensitive element, causing multiple elastic beams to undergo tangential bending deformation, and forming a tangential strain signal corresponding to the friction torque at the strain gauge;

[0018] Step S5, Loading and Synchronous Acquisition: Adjust the overflow valve to the target load pressure. After the speed, pressure, and bridge output signals stabilize, use the signal acquisition card to synchronously acquire the first Wheatstone full-bridge output voltage U. A The second Wheatstone full-bridge output voltage U B Pressure sensor signal and speed sensor signal;

[0019] Step S6, Frictional Torque Calculation: The first Wheatstone full-bridge output voltage U obtained synchronously is used as the frictional torque calculation. A Second Wheatstone full-bridge output voltage U B Zero-point subtraction, same-polarity superposition, and signal amplification are performed to obtain the output voltage U of the friction torque channel. out :

[0020] ;

[0021] Where G is the signal conditioning amplification factor, and U A0 and U B0 These are the initial zero-point voltages of the first and second Wheatstone bridges under frictionless torque conditions, respectively.

[0022] Calculate the friction torque of the slipper:

[0023] ;

[0024] in, K is the friction torque of the slipper, and K is the friction torque-voltage calibration coefficient.

[0025] Step S7, Stop and Unload: After the test is completed, adjust the overflow valve to reduce the system pressure to an unloaded state, the motor decelerates and stops, and the power is cut off.

[0026] As a further improvement of the present invention, in step S4, the frictional torque is equivalent to the tangential component acting on each elastic beam, wherein the tangential component satisfies:

[0027] ;

[0028] in, The tangential component of the force borne by a single elastic beam. Let n be the friction torque of the slipper, n be the number of elastic beams, and R be the effective radius from the line of action of the equivalent tangential component force on each elastic beam to the central axis of the elastic sensitive element.

[0029] As a further improvement of the present invention, in step S3, the in-situ static calibration is performed by loading along the positive friction torque direction and the negative friction torque direction, and is held at each standard load point for a predetermined time. The average value of the corresponding full-bridge output voltage stable segment is taken as the calibration output voltage of the standard load point.

[0030] As a further improvement of the present invention, in step S3, the standard friction torque is determined by the product of the standard load and the standard lever arm length, and the output voltage is calibrated according to multiple standard friction torque values ​​and their corresponding friction torque channels. The friction torque-voltage calibration coefficient K is obtained by linear fitting or least squares method.

[0031] As a further improvement of the present invention, in step S5, the motor spindle speed is first increased to the preset operating speed and kept stable, and then the overflow valve is adjusted to the target load pressure. After the speed signal, pressure signal and bridge output signal are all stable, synchronous acquisition is performed.

[0032] As a further improvement of the present invention, in step S6, after the host computer performs low-pass filtering and periodic synchronous averaging on the output voltage of the friction torque channel, it calculates the slipper friction torque according to the friction torque-voltage calibration coefficient K.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. This invention uses the swashplate as a transmission component for the frictional action of the slipper and connects the back of the swashplate to an elastic sensitive element, so that the frictional torque generated between the slipper and the swashplate can be directly converted into the tangential bending strain signal of the elastic beam. This enables direct and real-time measurement of the slipper frictional torque, avoiding the errors caused by indirect estimation based solely on the power loss of the entire pump or empirical models.

[0035] 2. The elastic sensing element of the present invention adopts a structure consisting of an inner hub, an outer hub, and multiple radial elastic beams, which can improve the strain response sensitivity to friction torque around the central axis while ensuring the support stiffness of the swashplate. This is beneficial for obtaining stable and distinguishable friction torque measurement signals under high pressure and high speed conditions.

[0036] 3. This invention arranges strain gauges on an elastic beam to form a Wheatstone bridge, so that the tangential bending strain caused by frictional torque is differentially superimposed and output. At the same time, it can suppress interference signals generated by non-frictional loads such as axial hydraulic load, overturning moment and installation error, thereby improving the accuracy and reliability of frictional torque measurement.

[0037] 4. The present invention is equipped with a hydraulic loading unit, which establishes different load pressures by adjusting the relief valve, and collects data synchronously with the speed sensor, pressure sensor and signal acquisition card. It can test the slipper friction torque under different speeds and load pressures, which is closer to the actual working state of the axial piston pump.

[0038] 5. This invention adopts an in-situ static calibration method, which establishes the calibration relationship between friction torque and voltage output before measurement, and calculates the slipper friction torque according to the calibration coefficient in actual testing. This reduces the impact of assembly errors, sensor sensitivity differences and structural processing deviations on the measurement results, and improves the repeatability and engineering applicability of the test results. Attached Figure Description

[0039] Figure 1 This is a structural diagram of the high-pressure axial piston pump slipper friction torque measuring device of the present invention.

[0040] Figure 2 This is a schematic diagram of the elastic sensitive element structure in the measuring device of the present invention.

[0041] Figure 3 This is a schematic diagram showing the arrangement of the strain gauges of the present invention on the elastic beam.

[0042] Figure 4 This is a flowchart of the high-pressure axial piston pump slipper friction torque measurement method of the present invention.

[0043] Explanation of reference numerals in the attached drawings: 1-Motor, 2-Coupling, 3-Speed ​​sensor, 4-Shaft, 5-Cylinder block, 6-Plunger, 7-Slipper, 8-Swashplate, 9-Pin, 10-Housing, 11-Screw, 12-Strain gauge, 13-Elastic sensitive element, 131-Outer hub, 132-Inner hub, 133-Elastic beam, 14-Signal acquisition card, 15-Host computer, 16-Reset spring, 17-Check valve, 18-Pressure sensor, 19-Relief valve, 20-Oil tank. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0045] like Figure 1 As shown, this invention proposes a high-pressure axial piston pump slipper friction torque measuring device, including a testing unit and a signal acquisition and processing unit. Specifically, the testing unit includes a motor 1, a cylinder 5, a swashplate 8, an elastic sensing element 13, and a housing 10. The motor 1 is connected to the main shaft of the cylinder 5 via a coupling 2, driving the cylinder 5 to rotate. Multiple pistons 6 are arranged circumferentially within the cylinder 5. The head of each piston 6 is connected to a slipper 7. The slipper 7 and the swashplate 8 are slidably connected via an oil film, together forming a slipper pair.

[0046] like Figure 2 As shown, the elastic sensing element 13 includes an outer hub 131 and an inner hub 132, which are coaxially arranged. The inner hub 132 is fixedly connected to the back of the swashplate 8 from the front end via a pin 9, and the outer hub 131 is fixedly connected to the housing 10 from the rear end via screws 11. The outer hub 131, inner hub 132, and elastic beams 133 are all made of carbon structural steel. Multiple circumferentially distributed elastic beams 133 connect the outer hub 131 and inner hub 132, extending radially. The central axis of the elastic sensing element 13 is taken as the Z-axis. For any elastic beam 133, L represents the effective beam length of the elastic beam 133 between the inner hub 132 and the outer hub 131, B represents the width of the rectangular cross-section of the elastic beam 133, and H represents the cross-sectional height of the elastic beam 133 along the Z-axis. The elastic beam 133 extends from the inner hub 132 to the outer hub 131 along its effective beam length. The frictional torque of the slipper 7 is transmitted to the elastic beam 133 through the swashplate 8 and the inner hub 132, causing the elastic beam 133 to undergo tangential bending deformation. Strain gauges 12 are disposed on the sides of the elastic beam 133 in the width direction to sense the tensile strain and compressive strain generated by the tangential bending deformation, respectively.

[0047] Preferably, the cross-section of the elastic beam 133 is designed as a rectangle with a height-to-width ratio, meaning that the height H along the axial direction is much greater than the width B along the tangential direction. Specifically, H / B is 2 to 10, preferably 3 to 6.

[0048] The signal acquisition and processing unit includes a speed sensor 3, a signal acquisition card 14, and a host computer 15. The speed sensor 3 is installed on the shaft of the motor 1. The speed sensor 3 and the strain gauge 12 are both electrically connected to the signal acquisition card 14. The signal acquisition card 14 (also known as a high-speed acquisition card) is used to acquire the speed of the motor 1 and the signal of the strain gauge 12 and upload them to the host computer 15 for processing.

[0049] The measuring device also includes a hydraulic loading unit, which includes a pressure sensor 18 and a relief valve 19. The relief valve 19 is connected to the oil outlet of the plunger 6. The pressure sensor 18 is installed on the oil line to monitor the discharge pressure. By adjusting the relief pressure of the relief valve 19, the load of the plunger 6 under different working conditions can be simulated.

[0050] Specifically, the oil suction and discharge process of the hydraulic loading unit is as follows: When the cylinder 5 rotates and the plunger 6 is in the suction stroke, the return spring 16 pushes the plunger 6 outward and keeps the slipper 7 in follow-up contact with the swashplate 8. The volume of the plunger cavity increases accordingly, and the pressure inside the cavity decreases. At this time, oil enters the plunger 6 through the check valve 17. The check valve 17 is used to prevent the high-pressure oil in the plunger cavity from flowing back into the suction line during the discharge stroke. When the cylinder 5 continues to rotate and the plunger 6 is in the discharge stroke, the plunger 6 and the slipper 7 return to the plunger cavity under the action of the swashplate 8. The volume of the plunger cavity decreases, and the oil in the cavity enters the loading oil circuit through the discharge port. The pressure sensor 18 is used to monitor the discharge pressure in the loading oil circuit in real time. The outlet of the relief valve 19 is connected to the oil tank 20. By adjusting the relief pressure of the relief valve 19, a stable back pressure is formed on the discharge side, thereby simulating the working state of the slipper under different load pressure conditions.

[0051] In this embodiment, there are four elastic beams, forming a cross-shaped structure between the outer hub and the inner hub.

[0052] The mechanical model and measurement principle of the elastic sensing element 13 are as follows:

[0053] The elastic sensing element 13 includes an outer hub 131, an inner hub 132, and four elastic beams 133 connecting the two. The four elastic beams 133 are arranged at 90° intervals about the central axis of the elastic sensing element 13. The geometric dimensions, material parameters, and strain gauge 12 bonding positions of each elastic beam 133 are kept consistent to ensure that each measurement branch has basically consistent mechanical response characteristics.

[0054] Based on the aforementioned rectangular cross-section with a height-to-width ratio of the elastic beam 133, the elastic beam 133 exhibits differentiated stiffness characteristics under different loads. When the axial hydraulic thrust generated by the plunger 6 acts on the swashplate 8 and is transmitted to the elastic sensing element 13, the elastic beam 133 primarily relies on the height H of the rectangular cross-section to provide bending stiffness. At this time, the moment of inertia of the bending section corresponding to the elastic beam 133 can be calculated as follows: I a The moment of inertia of the bending section of the elastic beam 133 under axial hydraulic thrust is given. Since H is large, the moment of inertia in this direction is also large. Therefore, the elastic beam 133 has high load-bearing stiffness under axial hydraulic thrust, which can reduce the influence of axial load on the friction torque measurement signal. When friction occurs between the slipper 7 and the swashplate 8, the frictional force forms a frictional torque around the central axis of the elastic sensing element 13 on the swashplate 8. This frictional torque is transmitted to the four elastic beams 133 through the inner hub 132, causing the elastic beams 133 to undergo tangential bending deformation. At this time, the moment of inertia of the bending section corresponding to the elastic beam 133 can be calculated as follows: I t Let B be the moment of inertia of the bending section of the elastic beam 133 when it is subjected to frictional torque and undergoes tangential bending. Since B is small, the moment of inertia of the section in this direction is small. Therefore, the elastic beam 133 has high strain sensitivity to frictional torque and can effectively convert the frictional torque of the slipper into a measurable strain signal.

[0055] Therefore, the cross-shaped elastic sensing element 13 can improve the detection sensitivity of the slipper friction torque while maintaining high axial load stiffness, and is conducive to reducing the interference of non-friction loads such as axial load and overturning moment on the measurement results.

[0056] When the slipper 7 rotates with the cylinder 5 on the surface of the swashplate 8 and generates friction, the slipper friction force acts on the swashplate 8, forming a frictional torque around the central axis of the elastic sensing element 13. This frictional torque is transmitted through the swashplate 8 to the inner hub 132 of the elastic sensing element 13, causing the inner hub 132 to rotate slightly relative to the outer hub 131, thereby causing the four elastic beams 133 connected between the inner hub 132 and the outer hub 131 to undergo tangential bending deformation. The strain gauges 12 attached to the two sides of the elastic beams 133 in the width direction generate tensile strain and compressive strain respectively, and form a differential output through a Wheatstone full-bridge circuit, thereby converting the slipper friction torque into an acquireable voltage signal.

[0057] Strain gauge 12 is connected to signal acquisition card 14 via bridge excitation power supply and signal conditioning amplifier. Signal acquisition card 14 synchronously samples the full-bridge output voltage, the pressure signal output by pressure sensor 18, and the speed pulse signal output by speed sensor 3 under the same clock. Host computer 15 performs zero-point subtraction, low-pass filtering, periodic synchronous averaging, and cross-sensitivity compensation on the acquired voltage signal, and calculates the slipper friction torque based on the friction torque-voltage calibration coefficient obtained from in-situ calibration. Specifically, the sampling frequency is not less than 10 times the slipper passing frequency, the bridge power supply is constant voltage excitation or constant current excitation, and the signal conditioning module includes a low-pass filter circuit and a differential amplifier circuit.

[0058] like Figure 3 As shown, this embodiment uses two Wheatstone bridges. Taking the positive frictional torque as the defined direction, strain gauges with increased resistance under the action of frictional torque are denoted as "+ΔR", and strain gauges with decreased resistance are denoted as "-ΔR". Four strain gauges on a pair of opposing elastic beams distributed along the Y-axis constitute the first Wheatstone bridge, and four strain gauges on a pair of opposing elastic beams distributed along the X-axis constitute the second Wheatstone bridge; the output voltages of the two bridges are denoted as U... A and U B After summing in phase, the friction torque channel output U is obtained. out .

[0059] To further clarify the connection positions of each strain gauge in the full-bridge circuit and their corresponding stress states, the wiring relationships of the first and second Wheatstone full-bridge circuits are explained below. The first Wheatstone full-bridge corresponds to a pair of relatively elastic beams distributed along the Y-axis, and the second Wheatstone full-bridge corresponds to a pair of relatively elastic beams distributed along the X-axis. Each strain gauge is connected to a bridge arm with a corresponding output polarity according to its tensile or compressive state under the action of positive frictional torque, thereby causing the strain signal caused by the frictional torque to form a differential superposition in the full-bridge output. The specific wiring relationship of the first Wheatstone full-bridge is shown in Table 1.

[0060] Table 1

[0061]

[0062] Similar to the first Wheatstone bridge, the second Wheatstone bridge is used to collect tangential bending strain signals on a pair of relatively elastic beams distributed along the X-axis. Their wiring relationship is determined according to the same differential superposition principle, as shown in Table 2.

[0063] Table 2

[0064]

[0065] Based on the above bridge arm connection relationship, when the elastic beam undergoes tangential bending deformation under the action of frictional torque, the resistance value of each strain gauge will change with the tensile or compressive strain at its location. The change in resistance of the strain gauge and the strain satisfy the following relationship:

[0066] ;

[0067] Where ΔR is the change in strain gauge resistance, R0 is the initial resistance under strain, and K s ε is the strain gauge sensitivity coefficient, and ε is the strain at the location of the strain gauge.

[0068] For the first Wheatstone bridge, let the resistance changes of the strain gauges corresponding to the bridge arms A1, A2, A3, and A4 be ΔR respectively. A1 ΔR A2 ΔR A3 and ΔR A4 Then the output voltage U of the first Wheatstone full bridge A The expression is:

[0069] .

[0070] For the second Wheatstone bridge, similarly, let the resistance changes of bridge arms B1, B2, B3, and B4 be ΔR respectively. B1 ΔR B2 ΔR B3 and ΔR B4 Its output voltage U B The expression is:

[0071] ;

[0072] Among them, U ex This is the bridge circuit excitation voltage.

[0073] After zero-point subtraction and same-polarity superposition of the output voltages of the first and second Wheatstone full bridges, the total output voltage U of the friction torque channel is obtained by amplification through the signal conditioning module. out

[0074] ;

[0075] Where G is the signal conditioning amplification factor, and U A0 and U B0 These are the initial zero-point voltages of the first and second Wheatstone bridges under frictionless torque conditions, respectively.

[0076] The aforementioned wiring relationship allows the frictional torque signal around the central axis of the elastic sensing element 13 to be superimposed and output in each bridge arm. When the elastic sensing element 13 mainly bears the axial load, each strain gauge produces approximately unidirectional strain, which cancels out as a common-mode signal in adjacent bridge arms. When the elastic sensing element 13 bears the overturning moment, the strain gauges on the symmetrically positioned elastic beam 133 produce opposite deformations, which are canceled out by the symmetrical bridge arms or further canceled out when the outputs of the two full bridges are summed. Thus, the two sets of Wheatstone full bridges can enhance the effective signal corresponding to the frictional torque and reduce the interference of axial load and overturning moment on the frictional torque channel.

[0077] like Figure 4 As shown, this invention also proposes a method for measuring the frictional torque of a high-pressure axial piston pump slipper. This method converts the slipper friction into a frictional torque on the swashplate, then converts this frictional torque into a tangential bending strain signal of an elastic sensitive element, and obtains the correspondence between the voltage signal and the frictional torque through in-situ calibration, thereby achieving real-time measurement of the frictional torque of the high-pressure axial piston pump slipper.

[0078] Specifically, the method includes the following steps:

[0079] Step S1, Installation and Zeroing: Rigidly connect the back of the swashplate to the inner hub of the elastic sensing element, and fix the outer hub of the elastic sensing element to the housing, so that the swashplate forms an elastic connection support through the elastic sensing element; connect each strain gauge to the Wheatstone full-bridge circuit and connect the signal acquisition card; perform zero-point adjustment after the system is powered on and preheated.

[0080] Step S2, Strain Gauge Full Bridge Assembly and Decoupling Settings: Four strain gauges on a pair of opposing elastic beams distributed along the Y-axis constitute the first Wheatstone full bridge, and four strain gauges on a pair of opposing elastic beams distributed along the X-axis constitute the second Wheatstone full bridge. Using the positive frictional torque as the agreed direction, the strain gauges on the tension side (resistance increases under the positive frictional torque) are connected to the bridge arm with positive output polarity, and the strain gauges on the compression side (resistance decreases) are connected to the bridge arm with negative output polarity, so that the tangential bending strain caused by the frictional torque is differentially superimposed in the full bridge output. The output voltages of the first and second Wheatstone full bridges are denoted as U. A and U B , for U A and U B After polarity unification processing, summation and amplification are performed to obtain the output voltage U of the friction torque channel. out This enhances the effective signal of frictional torque and significantly suppresses interference signals caused by axial load and overturning moment.

[0081] Specifically, when the elastic sensing element 13 is subjected to the axial hydraulic thrust generated by the plunger, the strain gauges 12 on each elastic beam 133 produce approximately unidirectional strain, and the unidirectional strain cancels out as a common-mode signal in the full-bridge circuit; when the elastic sensing element 13 is subjected to an overturning moment about the X-axis or Y-axis, the strain gauges 12 on the relatively positioned elastic beam 133 produce opposite deformations, and the opposite deformations are canceled out by the symmetrical bridge arms, or canceled out after the two full-bridge outputs are summed; when the elastic sensing element 13 is subjected to a slipper friction torque about the Z-axis, the tangential bending strain of each elastic beam 133 forms a differential output in the full-bridge circuit.

[0082] Step S3: Before measurement, in-situ static calibration is required. During calibration, lock the pump spindle to ensure the swashplate 8 is stationary. Install a calibration plate or calibration base coaxial with the swashplate 8, and connect a length L to the calibration plate. b A standard lever arm. A standard load F is applied in stages at the end of the lever arm along a direction perpendicular to the tangential direction. i This causes the i-th load point to generate the corresponding standard frictional torque T. i T i According to standard load F i With lever arm length L b The product is determined, i.e., T i =F i L b During calibration, loads are applied along both the positive and negative torque directions, and each load point is held for a predetermined time. The average value U of the stable segment of the corresponding full-bridge output voltage is recorded. i The average value U of the stable segment i The output voltage of the friction torque channel obtained after zero-point subtraction, polarity homogenization superposition, and signal amplification of the output voltages of each Wheatstone full-bridge is calibrated. Based on multiple standard friction torques T... i and its corresponding friction torque channel calibration output voltage U i The friction torque-voltage calibration coefficient K is obtained by linear fitting or least squares method.

[0083] Step S4: After zeroing and calibration, start motor 1 and rotate cylinder 5, causing plunger 6 to drive slipper 7 to slide on the surface of swashplate 8. Slipper 7 generates friction under oil film support and load, which acts on swashplate 8 and forms a frictional torque. The frictional torque is transmitted to the elastic sensing element 13 via the swashplate 8, causing the inner hub 132 of the elastic sensing element 13 to rotate slightly relative to the outer hub 131. This, in turn, causes the multiple elastic beams 133 evenly distributed along the circumference to undergo tangential bending deformation. The strain gauges 12 mounted on the elastic beams 133 sense this tangential bending deformation and output a resistance change signal corresponding to the frictional torque, which is converted into a voltage signal via a Wheatstone full-bridge circuit.

[0084] In the conversion relationship between frictional torque and strain, the frictional torque of the slipper 7 can be equivalent to the tangential component acting on each elastic beam. Let the number of elastic beams 133 be... The effective radius from the line of action of the equivalent tangential component force of each elastic beam 133 to the central axis of the elastic sensitive element 13 is: The tangential component of the force borne by a single elastic beam 133 is Then we have:

[0085] ; in, The total frictional torque generated by the slipper 7 For the number of elastic beams, The effective radius of the line of action of the equivalent tangential component force of each elastic beam to the central axis of the elastic sensitive element 13.

[0086] Step S5, Loading and Synchronous Acquisition: During the measurement process, the spindle speed is steadily increased to the preset operating speed and maintained. Then, the overflow valve 19 is adjusted to the target load pressure to simulate the working state of the axial piston pump under different pressure conditions. After the speed, pressure, and bridge output signals are all stable, the output voltage U of the first Wheatstone full bridge is synchronously acquired using the signal acquisition card 14. A The second Wheatstone full-bridge output voltage U B Pressure sensor signal and speed sensor signal.

[0087] Step S6, Friction Torque Calculation: The synchronously acquired first and second Wheatstone full-bridge output voltages are subjected to zero-point subtraction, same-polarity superposition, and signal amplification to obtain the friction torque channel output voltage. for:

[0088] ;

[0089] Where G is the signal conditioning amplification factor, and U A0 and U B0 These are the initial zero-point voltages of the first and second Wheatstone bridges under frictionless torque conditions, respectively.

[0090] Therefore, the full-bridge output voltage is related to the tangential bending strain caused by the frictional torque, which can be combined with the frictional torque-voltage calibration coefficient obtained from the in-situ static calibration. The friction torque of the slip shoe under actual working conditions can then be calculated:

[0091] ;

[0092] in, For the friction torque of the slipper, The friction torque-voltage calibration coefficient is obtained from in-situ static calibration.

[0093] Step S7, Stop and Unload: After the test is completed, first adjust the relief valve 19 to gradually reduce the system pressure, so that the hydraulic system returns to the no-load state; then control the motor 1 to decelerate and stop rotating, and finally cut off the power to end the measurement. Through the above measurement method, the friction of the slipper 7 can be converted into an acquireable voltage signal in real time without significantly damaging the original lubrication and stress state of the slipper 7, and the friction torque of the slipper 7 can be obtained through calibration calculation, thereby realizing the direct measurement of the friction characteristics of the slipper 7 under high pressure, variable speed and variable load conditions.

[0094] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Various changes that can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention are within the protection scope of the claims of the present invention.

Claims

1. A high pressure axial piston pump shoe friction torque measuring device, characterized by, include: The testing unit includes a motor, a cylinder, a swashplate, an elastic sensing element, and a housing. The motor is connected to the cylinder's main shaft, driving the cylinder to rotate. Multiple plungers are circumferentially arranged within the cylinder, each plunger's head connected to a sliding shoe. An oil film is formed between the sliding shoe and the swashplate's working surface, allowing the sliding shoe to slide along the swashplate's working surface under the support of the oil film. The elastic sensing element includes an outer hub and an inner hub, concentrically arranged. The inner hub is fixedly connected to the back of the swashplate from its front end, and the outer hub is fixedly connected to the housing from its rear end. Multiple radially extending elastic beams are provided between the outer and inner hubs, each elastic beam equipped with a strain gauge for detecting tangential bending strain. The strain gauges form a Wheatstone bridge, superimposing and outputting the strain signals caused by frictional torque. The signal acquisition and processing unit includes a speed sensor, a signal acquisition card, and a host computer. The speed sensor is installed on the motor shaft. Both the speed sensor and the strain gauge are electrically connected to the signal acquisition card. The signal acquisition card is used at least to acquire the motor speed and strain gauge signals and upload them to the host computer for processing.

2. The high pressure axial piston pump shoe friction torque measuring device of claim 1, wherein, It also includes a hydraulic loading unit, which includes a pressure sensor and a relief valve. One end of the relief valve is connected to the plunger outlet oil circuit, and the other end is connected to the oil tank. The pressure sensor is set in the loading oil circuit between the plunger cavity oil port and the relief valve inlet to monitor the discharge pressure. By adjusting the relief valve overflow pressure, the load of the plunger under different working conditions can be simulated.

3. The high pressure axial piston pump shoe friction torque measuring device of claim 2, wherein, With the central axis of the elastic sensitive element as the Z-axis, the radial extension direction of the elastic beam between the inner and outer hubs as the beam length direction, and the cross-section of the elastic beam perpendicular to the beam length direction as a rectangle, the side length of the rectangular cross-section along the Z-axis direction is greater than the side length perpendicular to the beam length direction.

4. The high pressure axial piston pump shoe friction torque measuring device of claim 3, wherein, The number of elastic beams is four, forming a cross-shaped structure between the outer hub and the inner hub.

5. A method for measuring the frictional torque of a high-pressure axial piston pump slipper, employing the high-pressure axial piston pump slipper frictional torque measuring device as described in claim 4, characterized in that... The method includes the following steps: Step S1, Installation and Zeroing: Rigidly connect the back of the swashplate to the inner hub of the elastic sensing element, and fix the outer hub of the elastic sensing element to the housing, so that the swashplate forms an elastic connection support through the elastic sensing element; connect each strain gauge to the Wheatstone full-bridge circuit and connect the signal acquisition card; perform zero-point adjustment after the system is powered on and preheated. Step S2, Strain Gauge Full Bridge Assembly and Decoupling Settings: A pair of strain gauges distributed along the first radial direction on opposite elastic beams form a first Wheatstone full bridge, and a pair of strain gauges distributed along the second radial direction orthogonal to the first radial direction on opposite elastic beams form a second Wheatstone full bridge; the strain gauges on the tension side and the compression side of the elastic beams under tangential bending are respectively connected to the corresponding bridge arms of the full bridge circuit, so that the tangential bending strain caused by the frictional torque forms a differential superposition in the full bridge output, and the unidirectional strain caused by the axial load and the symmetrical strain caused by the overturning moment cancel each other out in the full bridge output; Step S3, In-situ Static Calibration: Lock the pump spindle, install a standard lever arm at a position coaxial with the swashplate, apply standard loads step by step along the tangential direction to generate multiple known standard friction torque values, record the friction torque channel calibration output voltage after zero-point subtraction, polarity unification superposition and signal amplification processing of the corresponding full-bridge output voltage, and obtain the friction torque-voltage calibration coefficient K by fitting; Step S4, Friction Torque-Strain Conversion: Start the motor and drive the cylinder to rotate, so that the head of the plunger drives the slipper to slide on the surface of the swashplate; the friction force generated by the slipper acts on the swashplate and forms a friction torque, which is transmitted through the swashplate to the inner hub of the elastic sensitive element, causing multiple elastic beams to undergo tangential bending deformation, and forming a tangential strain signal corresponding to the friction torque at the strain gauge; Step S5, Loading and Synchronous Acquisition: Adjust the overflow valve to the target load pressure. After the speed, pressure and bridge output signals stabilize, use the signal acquisition card to synchronously acquire the first Wheatstone full bridge output voltage UA, the second Wheatstone full bridge output voltage UB, the pressure sensor signal and the speed sensor signal. Step S6, Friction Torque Calculation: The synchronously acquired first Wheatstone full-bridge output voltage UA and second Wheatstone full-bridge output voltage UB are subjected to zero-point subtraction, same-polarity superposition, and signal amplification to obtain the friction torque channel output voltage Uout. ； Where G is the signal conditioning amplification factor, and UA0 and UB0 are the initial zero-point voltages of the first and second Wheatstone full bridges under frictionless torque conditions, respectively. Calculate the friction torque of the slipper: ； in, K is the friction torque of the slipper, and K is the friction torque-voltage calibration coefficient. Step S7, Stop and Unload: After the test is completed, adjust the overflow valve to reduce the system pressure to an unloaded state, the motor decelerates and stops, and the power is cut off.

6. The method for measuring the frictional torque of the slipper of a high-pressure axial piston pump according to claim 5, characterized in that, In step S4, the frictional torque is equivalent to the tangential component acting on each elastic beam, and the tangential component satisfies: ； in, The tangential component of the force borne by a single elastic beam. Let n be the friction torque of the slipper, n be the number of elastic beams, and R be the effective radius from the line of action of the equivalent tangential component force on each elastic beam to the central axis of the elastic sensitive element.

7. The method for measuring the frictional torque of the slipper of a high-pressure axial piston pump according to claim 5, characterized in that, In step S3, the in-situ static calibration is performed by loading along the positive friction torque direction and the negative friction torque direction, respectively, and holding at each standard load point for a predetermined time. The average value of the corresponding full-bridge output voltage stable segment is taken as the calibration output voltage of that standard load point.

8. The method for measuring the frictional torque of the slipper of a high-pressure axial piston pump according to claim 5, characterized in that, In step S3, the standard friction torque is determined by the product of the standard load and the standard lever arm length, and the output voltage is calibrated based on multiple standard friction torque values ​​and their corresponding friction torque channels. The friction torque-voltage calibration coefficient K is obtained by linear fitting or least squares method.

9. The method for measuring the frictional torque of the slipper of a high-pressure axial piston pump according to claim 5, characterized in that, In step S5, the motor spindle speed is first increased to the preset operating speed and kept stable. Then the overflow valve is adjusted to the target load pressure. After the speed signal, pressure signal and bridge output signal are all stable, synchronous acquisition is performed.

10. The method for measuring the frictional torque of the slipper of a high-pressure axial piston pump according to claim 5, characterized in that, In step S6, the host computer performs low-pass filtering and periodic synchronous averaging on the output voltage of the friction torque channel, and then calculates the slipper friction torque based on the friction torque-voltage calibration coefficient K.

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