A piston skirt oil film thickness transient measurement device

Abstract

The application discloses a kind of piston skirt oil film thickness transient measurement device, belong to piston and cylinder liner between oil film thickness measurement control field.The application includes in-cylinder system power module, capacitive sensor, capacitive acquisition module, acceleration acquisition module, memory module, main controller, wireless transmission module, host computer data processing module, modified piston.Modified piston is the piston of installation capacitive sensor to make adaptive improvement processing, to install capacitive sensor probe, improvement processing includes drilling, grinding.The application adds acceleration sensor in existing piston skirt oil film thickness measurement device, under fixed speed condition, measure piston skirt oil film thickness each time while measuring piston axial acceleration, process piston axial acceleration data to obtain sampling point crank angle position, so that oil film thickness telemetry device can obtain the numerical value of oil film thickness at different crank angle positions, with the advantages of accurate measurement of crank angle, without changing engine mechanical structure.

Description

TECHNICAL FIELD

[0001] The application relates to a piston skirt oil film thickness transient measurement device and belongs to the technical field of oil film thickness measurement and control between a piston and a cylinder sleeve. BACKGROUND

[0002] An engine is the heart of a vehicle and converts chemical energy of fuel into mechanical energy to provide power for the vehicle. A combustion chamber composed of a piston, a cylinder cover and a valve bears a large thermal load, and a piston and a piston ring set not only bear the thermal load but also are subjected to strong friction and wear, so the piston and the piston ring set are the most severe working environment parts in the engine, and the performance of the piston and the piston ring set has a decisive influence on the performance of the engine. The piston reciprocates at a high speed in the cylinder sleeve, and the piston surface is subjected to strong friction, and a lubricating oil film can change the friction into fluid friction to reduce the wear of the piston and the piston ring. With the development of science and technology, the performance of a diesel engine develops towards high speed and heavy load. Under the high speed and heavy load working conditions, the impact load of the piston on the cylinder sleeve is stronger, the pressure between the piston and the cylinder sleeve is larger, the lubricating oil film is thinned or even broken under high pressure, the wear of the piston and the piston ring is increased, and the service life of the piston and the piston ring is reduced.

[0003] Under the background that the engine develops towards high speed and heavy load, a large number of scholars have carried out relevant researches on piston friction, and the lubrication monitoring technology of the piston and the piston ring set is widely researched. The oil film thickness measurement technology of the piston skirt and the piston ring is developed earlier and has many types. The film thickness measurement technologies mainly include an optical method, an electrical method and an ultrasonic method, the optical method includes an optical interference method, a laser-induced fluorescence method and an X-ray method, the electrical method includes a resistance method, a capacitance method and a magnetic resistance method. The capacitance method is a relatively mature method, has a simple measurement principle and high precision in measuring micron-level oil film thickness.

[0004] The existing piston transient telemetry technology only increases a sampling frequency relative to the steady-state telemetry technology, obtains transient changes of piston parameters in the running process, and reversely calculates a crank angle position through the measured parameter changes. The above method is relatively practical for measuring parameters such as temperature which can obviously reflect the crank angle, but the oil film thickness of the piston skirt changes complexly during engine operation, and the change trend of the measurement result cannot reversely calculate the crank angle, so the crank angle position needs to be accurately measured while the thickness is measured. SUMMARY

[0005] In order to solve the problem that the existing piston skirt oil film thickness measurement device based on the capacitive method fails to measure the piston crank angle position, the present application mainly aims to provide a piston skirt oil film thickness transient measurement device, which adds an acceleration sensor in the existing piston skirt oil film thickness measurement device, measures the piston skirt oil film thickness and the piston axial acceleration at the same time under the condition of a fixed rotating speed, processes the piston axial acceleration data to obtain the crank angle position at the sampling point, and enables the oil film thickness telemetry device to obtain the values of the oil film thickness at different crank angle positions, thereby having the advantages of accurate measurement of the crank angle and no need to change the mechanical structure of the engine.

[0006] The object of the present application is achieved by the following technical solutions.

[0007] The present application discloses a piston skirt oil film thickness transient measurement device, which comprises an in-cylinder system power module, a capacitive sensor, a capacitive acquisition module, an acceleration acquisition module, a memory module, a main controller, a wireless transmission module, an upper computer data processing module and a modified piston.

[0008] The in-cylinder system power module supplies power to the capacitive acquisition module, the acceleration acquisition module, the memory module, the main controller and the wireless transmission module, and mainly comprises a battery and a voltage stabilizing chip and its peripheral circuit.

[0009] The mechanical structure of the capacitive sensor comprises a capacitive electrode probe, a probe insulation sleeve, a brush, a spring and a brush support frame, and is used for converting the oil film thickness between the piston skirt and the cylinder sleeve into a capacitive signal. The capacitive electrode probe has a cylindrical overall shape, and the friction surface thereof is processed to have a surface curvature consistent with the piston skirt, so that the friction surface is aligned with the outer surface of the piston skirt when the capacitive electrode probe is installed on the piston, and a circumferential positioning structure is processed on the side surface of the capacitive electrode probe to cooperate with the inner surface of the probe insulation sleeve. The probe insulation sleeve is processed using an insulating material, and has a cylindrical main body with a through hole, and circumferential positioning structures are processed on the inner and outer surfaces. The brush support frame is made of an insulating material, one end of the brush support frame is processed to have a square hole for placing the brush, the other end is processed to have a diameter circular hole for placing the spring, and the main body has a cylindrical shape, and a radial hole is processed on the brush support frame for placing a wire. The brush has a wire, is placed in the square hole of the brush support frame and can move axially, and the brush wire is led out through the radial through hole of the brush support frame. The brush is pressed against the cylinder sleeve by the spring force and establishes an electrical connection with the cylinder sleeve.

[0010] The capacitive acquisition module is used for acquiring the capacitance value of the capacitive sensor and converting it into a digital signal.

[0011] The acceleration acquisition module comprises an acceleration sensor chip and is used for acquiring the piston axial acceleration.

[0012] The memory module refers to a non-volatile memory for temporarily storing signals collected by the main controller.

[0013] The main controller is used for receiving the capacitance signals and the acceleration signals and storing them into the memory module. When the main controller receives a wireless transmission instruction, the data is taken out from the memory and transmitted to the data processing module of the upper computer.

[0014] The wireless transmission module is used for transmitting data between the main controller and the data processing module of the upper computer.

[0015] The data processing module of the upper computer is used for receiving and storing the skirt point capacitance signals and the piston axial acceleration signals. The skirt point capacitance signals are processed by the parallel plate capacitor formula to obtain the oil film thickness of the measuring point. The piston axial acceleration signals are processed to determine the crankshaft angular position of each sampling point, thereby realizing transient measurement.

[0016] The modified piston is a piston which is adapted and improved for installing a capacitance sensor. Since the capacitance sensor is placed on the piston skirt, the piston is adapted and improved by punching and grinding to install the probe of the capacitance sensor.

[0017] The acceleration data is processed in the data processing module of the upper computer to obtain the crankshaft angular position, and the specific implementation method is as follows:

[0018] Step one, intercepting the acceleration scatter diagram in a single working cycle. Formula (1) is an approximate calculation formula of the piston axial acceleration

[0019] j = r · ω 2 · (cos α + λ · cos 2α) (1)

[0020] Wherein, j is the piston axial acceleration, r is the crank radius, ω is the engine speed, λ is the ratio of the crank radius and the connecting rod length, and α is the crankshaft angular position relative to the top dead center.

[0021] It is known from formula (1) that when the crankshaft drives the piston to move to the top dead center, the absolute value of the piston axial acceleration is maximum. The crankshaft continuously rotates, so the piston axial acceleration scatter diagram changes periodically, and the measurement result of the device ultimately reflects the oil film thickness change in a single working cycle. Therefore, the acceleration scatter diagram in a single working cycle is intercepted for processing to obtain the crankshaft angular position of the sampling point in the cycle.

[0022] Step two, fitting the acceleration scatter diagram in a single working cycle. According to formula (1), the maximum point of the absolute value of acceleration in the acceleration measurement scatter diagram is determined, that is, the top dead center position of the piston is obtained, but due to the random error of the acceleration sensor in measurement, the maximum point of the absolute value of acceleration cannot be accurately positioned, so the maximum point of the acceleration is determined by means of fitting curve. Formula (2) represents the relationship between the crank angle position and the angular velocity and time.

[0023] Alpha = omega * t (2)

[0024] Wherein, t is time.

[0025] Formula (2) is substituted into formula (1) to obtain formula (3).

[0026] J = r * omega 2 · (cos omega * t + lambda * cos 2 omega * t) (3)

[0027] Since the sampling time interval, the crank radius and the connecting rod length are known, and the actual speed is slightly different from the measured speed due to measurement error, the speed is taken as the fitting parameter, and the least square fitting of the acceleration scatter diagram is carried out using formula (3) to obtain the fitting curve.

[0028] Step three, the crank angle corresponding to each sampling point is determined by the fitting curve and formula (2). The maximum point of the absolute value of the fitting curve is positioned, and the nearest sampling point to the point is selected as the top dead center. The top dead center time is regarded as 0, and since the speed is constant, the sampling time interval is determined, and the crank angle of each sampling point in the working cycle is calculated by formula (2), that is, the crank angle corresponding to each sampling point in a single working cycle is determined.

[0029] Advantages:

[0030] 1. The piston skirt oil film thickness transient measurement device disclosed in the application increases the temperature measurement module and the acceleration measurement module compared with the existing capacitor method for measuring the piston skirt oil film thickness device, obtains the top dead center position through the acceleration measurement result curve, calculates the crank angle of each sampling point through formula, realizes the measurement function of the sampling point crank angle, can obtain the change curve of the oil film thickness in each engine working cycle, and realizes the transient measurement of the skirt oil film thickness.

[0031] 2. The piston skirt oil film thickness transient measurement device disclosed in the application temporarily saves the high-speed collected data by using a nonvolatile memory, reads the memory data at a lower frequency, uses wireless transmission, can ensure that the collected signal does not lose frames, and protects the integrity of the signal.

[0032] 3. The piston skirt oil film thickness transient measurement device disclosed in the present application determines the crank angle through axial acceleration, so that the sensors used for realizing the transient measurement function can be installed on the piston, and therefore the transient measurement can be realized by only machining the piston test sample, without the need of machining adaptation of other engine parts, thereby reducing the machining difficulty and cost. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The hardware overall framework of the piston skirt oil film thickness transient measurement device disclosed in the present embodiment.

[0034] Figure 2 The measurement flowchart of the piston skirt oil film thickness transient measurement device disclosed in the present embodiment.

[0035] Figure 3 The installation schematic diagram of the piston skirt oil film thickness transient measurement device disclosed in the present embodiment.

[0036] Figure 4 The modified piston and the three-dimensional machining model of the capacitor sensor of the piston skirt oil film thickness transient measurement device disclosed in the present embodiment.

[0037] Figure 5 The capacitor sensor assembly drawing of the piston skirt oil film thickness transient measurement device disclosed in the present embodiment.

[0038] Figure 6 The capacitor and acceleration sampling points under the condition of 800 rpm in the engine motoring bench test.

[0039] Figure 7 The acceleration fitting curve in a single period.

[0040] Figure 8 The oil film thickness transient measurement result in a single period under the condition of 800 rpm.

[0041] 1 - in-cylinder system power module, 2 - capacitor sensor, 2.1 - capacitor electrode probe, 2.2 - probe insulation sleeve, 2.3 - brush support frame, 2.4 - brush, 2.5 - spring, 3 - capacitor acquisition module, 4 - acceleration acquisition module, 5 - memory module, 6 - main controller, 7 - wireless transmission module, 8 - host computer data processing module, 9 - modified piston. DETAILED DESCRIPTION

[0042] The present application will now be further described in detail by reference to the drawings, which are simplified schematic diagrams, and only schematically show the basic structure of the present application and its working mode, and therefore only show the components related to the present application.

[0043] Example 1:

[0044] Figure 1 As shown in the piston skirt oil film thickness transient measurement device disclosed in the embodiment, the piston skirt oil film thickness transient measurement device comprises an in-cylinder system power module 1, a capacitance sensor 2, a capacitance collection module 3, an acceleration collection module 4, a memory module 5, a main controller 6, a wireless transmission module 7, an upper computer data processing module 8 and a modified piston 9.

[0045] The in-cylinder system power module 1 is used for supplying power to the capacitance collection module 2, the acceleration collection module 4, the memory module 5, the main controller 6 and the wireless transmission module 7, and is composed of an LTC3536 voltage stabilizing chip and a peripheral circuit thereof. Three automobile level button batteries BR2450A are connected in series to serve as a power supply for the LTC3536, and the LTC3536 voltage stabilizing chip outputs a 3.3V voltage.

[0046] The mechanical structure of the capacitance sensor 2 comprises a capacitance electrode probe 2.1, a probe insulation sleeve 2.2, a brush support frame 2.3, a brush 2.4 and a spring 2.5, and is used for converting the oil film thickness between the piston skirt and the cylinder sleeve into a capacitance signal. The capacitance electrode probe 2.1 is made of brass, and the probe surface has a diameter of 6mm. The friction surface thereof is processed to have a surface curvature consistent with the piston skirt, so that the friction surface is aligned with the outer surface of the piston skirt when the capacitance electrode probe 2.1 is installed on the piston. A circumferential positioning structure is processed on the side surface of the capacitance electrode probe 2.1, so that the capacitance electrode probe 2.1 cooperates with the inner surface of the probe insulation sleeve 2.2. The probe insulation sleeve 2.2 is made of engineering plastic, has a cylindrical main body, a through hole is processed, and a circumferential positioning structure is processed on the inner and outer surfaces. The brush support frame 2.3 is made of engineering plastic, a 6*4mm square hole is processed at one end of the brush support frame to place the brush 2.4, a 6mm diameter circular hole is processed at the other end to place the spring 2.5, the outer shape of the main body is a cylinder, one end of the square hole is processed into a straight slot shape, and a 2mm circular hole is punched along the radial direction at one end of the circular hole to place a lead wire. The brush 2.4 is made of a copper-containing carbon brush and has a lead wire, and the length, width and height thereof are selected to be 6*4*9mm. The brush 2.4 is placed in the square hole of the brush support frame and can move axially. The lead wire of the brush 2.4 is led out through the radial through hole of the brush support frame 2.3. The brush 2.4 is pressed against the cylinder sleeve by the spring force, and an electrical connection is established between the brush 2.4 and the cylinder sleeve. Figure 5 (c) The surface of the brush 2.4 is ground to reduce the surface area of the contact surface, so that the lubricating oil film is not easy to form when the brush 2.4 moves relative to the cylinder sleeve, and the stability of the electrical connection is ensured.

[0047] The capacitance collection module 3 adopts a PCAP01 capacitance signal collection chip, which is used for collecting the capacitance formed by the capacitance electrode probe 2.1 and the cylinder sleeve and storing the capacitance signal in the result register of the PCAP01. The capacitance electrode probe 2.1 is connected to the PCAP01 through a lead wire, and the cylinder sleeve is connected to the PCAP01 through the brush 2.4 and a lead wire.

[0048] The acceleration acquisition module 4 uses an acceleration sensor chip ADXL1003 for acquiring the piston axial acceleration, which outputs different analog voltage signals under different accelerations.

[0049] The memory module 5 uses a non-volatile memory CY15B102Q, which can use the serial communication technology SPI to perform data reading and saving operations on the chip, and is used for temporarily saving the signals collected by the main controller.

[0050] The main controller 6 uses an STM32 single-chip microcomputer, which uses an SPI peripheral to communicate with the PCAP01 capacitor signal acquisition chip and the CY15B102Q memory 5, for burning the firmware program of the PCAP01, selecting the working mode of the PCAP01 and reading the capacitor results by setting the registers of the PCAP01, using the internal ADC peripheral to collect the acceleration signals, and then saving the capacitor signals and the acceleration signals into the memory chip CY15B102Q in a certain format. When the main controller 6 receives a wireless transmission instruction, the data is taken out from the memory CY15B102Q and transmitted to the in-cylinder wireless transmission module 7 through the on-chip peripheral UART.

[0051] The wireless transmission module 7 uses a Zigbee wireless communication chip CC2530, which is mainly used for transmitting data between the STM32 main controller 6 and the upper computer data processing module 8. The Z-stack protocol stack is used as the program framework of the CC2530 to realize the function of transparent transmission of serial port data, which can transmit the data of the STM32 main controller 5 to the out-of-cylinder Zigbee node, and also can transmit the instructions of the upper computer data processing module 8 from the out-of-cylinder Zigbee node to the in-cylinder Zigbee node.

[0052] The upper computer data processing module 8 is a window form application written in C# language under the windows operating system. The entire program first initializes the window form components (such as buttons, serial port modules), and uses a serial port component to communicate with the Zigbee coordinator in the upper computer window form application. The implementation logic of the acquisition work is as follows: first, wait for the Zigbee coordinator to send the capacitor and acceleration signals, when the above signals are received, check the data format, if the format is incorrect, discard the data, continue to wait for the next Zigbee coordinator signal. If the format is correct, save the capacitor value and acceleration, and use the parallel plate capacitor formula to calculate the oil film thickness, and process the acceleration data to obtain the crank angle position, so as to realize the transient measurement of the oil film thickness.

[0053] The improved piston 9 is a piston which is adapted to be installed with a capacitive sensor.

[0054] The acceleration data is processed in the host computer data processing module to obtain the crank angle position, and the specific implementation method is as follows:

[0055] Step one, intercept the acceleration scatter diagram in a single working cycle. Figure 6 (b) The acceleration measurement scatter diagram for the uniform speed 770 rpm working condition can be seen to change periodically, when the acceleration reaches the maximum value, the piston reaches the vicinity of the top dead center, and the period time is the time used for one revolution of the crankshaft. The measurement result of the device needs to reflect the change of the oil film thickness in a single period, so the acceleration scatter diagram in a single period is intercepted for processing, and the intercepted part is as shown in Figure 7 .

[0056] Step two, fitting the acceleration scatter diagram in a single working cycle. The engine reverse-drag bench mechanical structure parameters used in the experiment are known, the crank radius is 0.065 m, and the connecting rod length is 0.237 m. However, the actual speed and the measured speed will be slightly different due to measurement error, so the speed is taken as the fitting parameter, and the least square fitting is performed on the acceleration scatter diagram using formula (3), and the fitting curve is as shown in Figure 7 .

[0057] Step three, determine the crank angle corresponding to each sampling point through the fitting curve and formula (2). The maximum point of the fitting formula is found in the 0 time range, the sampling point closest to the maximum value point in time is selected as the top dead center sampling point, and the time of this point is set to 0, the time of the subsequent sampling points is incremented by 1.7 ms according to the measurement time interval of the telemetry system, and finally the crank angle position of the subsequent sampling points is calculated using formula (2). The capacitance corresponding to the crank angle position is processed to calculate the oil film thickness, realize the transient measurement of the piston skirt oil film thickness, and draw the oil film thickness transient measurement curve as shown in Figure 8 .

[0058] The specific description described above, the purpose, technical device and beneficial effect of the application are described in detail, it should be understood that the above description is only a specific embodiment of the application, for explaining the application, and does not limit the protection scope of the application, any modification, equivalent replacement, improvement, etc. within the spirit and principle of the application, should be included in the protection scope of the application.

Claims

1. A piston skirt oil film thickness transient measurement device characterized by: The device comprises an in-cylinder system power module, a capacitance sensor, a capacitance acquisition module, an acceleration acquisition module, a memory module, a main controller, a wireless transmission module, an upper computer data processing module and a modified piston. The in-cylinder system power module supplies power to the capacitance acquisition module, the acceleration acquisition module, the memory module, the main controller and the wireless transmission module, and mainly comprises a battery and a voltage stabilizing chip and peripheral circuits thereof. The mechanical structure of the capacitance sensor comprises a capacitance electrode probe, a probe insulation sleeve, a brush, a spring and a brush support frame, and is used for converting the oil film thickness between the piston skirt and the cylinder liner into a capacitance signal. In the upper computer data processing module, the acceleration data is processed to obtain the crank angle position, and the specific implementation method is as follows: Step one, intercept the acceleration scatter diagram in a single working cycle; formula (1) is an approximate calculation formula of the axial acceleration of the piston j = r - ω 2 • (cos a + λ - cos 2a) (1) Wherein, j is the axial acceleration of the piston, r is the crank radius, ω is the engine speed, λ is the ratio of the crank radius and the connecting rod length, and α is the crank angle. From formula (1), when the piston is moved to the top dead center by the crank, the absolute value of the axial acceleration of the piston is maximum; the crank continuously rotates, so the acceleration scatter diagram of the piston is periodically changed, and the measurement result of the device ultimately reflects the change of the oil film thickness in a single working cycle, so the acceleration scatter diagram in a single working cycle is intercepted for processing to obtain the crank angle position of the sampling point in the cycle. Step two, fitting the acceleration scatter diagram in a single working cycle; from formula (1), the maximum value point of the absolute value of the acceleration in the acceleration measurement scatter diagram is determined, and the position of the maximum value point of the acceleration is determined by means of the fitting curve; formula (2) represents the relationship between the crank angle position and the angular velocity and the time. α=ω·t (2) Wherein, t is the time. Formula (2) is substituted into formula (1) to obtain formula (3); j = r - ω 2 • (cos ω - t + λ - cos 2ω - t) (3) Since the sampling time interval, the crank radius and the connecting rod length are known, and the actual speed is slightly different from the measured speed due to measurement error, the speed is taken as a fitting parameter, and the least square fitting of the acceleration scatter diagram is performed by using formula (3) to obtain a fitting curve. Step three, determining the crank angle corresponding to each sampling point through the fitting curve and formula (2); positioning the maximum value point of the absolute value of the fitting curve, selecting the sampling point closest to the point as the top dead center; regarding the time of the top dead center as 0, since the speed is constant and the sampling time interval is determined, the crank angle of each sampling point in the working cycle is calculated by formula (2), that is, the crank angle corresponding to each sampling point in a single working cycle is determined.

2. A piston skirt oil film thickness transient measurement device as in claim 1, characterized by: The capacitor electrode probe has a cylindrical overall shape, and the friction surface thereof is processed to have a surface curvature consistent with the piston skirt, so that the friction surface is aligned with the outer surface of the piston skirt when the capacitor electrode probe is installed on the piston, and a circumferential positioning structure is processed on the side surface of the capacitor electrode probe to cooperate with the inner surface of the probe insulation sleeve; the probe insulation sleeve is processed using an insulating material, has a cylindrical main body, a through hole, and circumferential positioning structures processed on the inner and outer surfaces; the brush support frame is made of an insulating material, has a square hole at one end for placing the brush and a diameter circular hole at the other end for placing the spring, has a cylindrical overall shape, and has a radial hole for placing a wire; the brush has a wire, is placed in the square hole of the brush support frame and can move axially, and the wire of the brush is led out through the radial hole of the brush support frame; the brush is pressed against the cylinder sleeve by the spring force and establishes an electrical connection with the cylinder sleeve.

3. A piston skirt oil film thickness transient measurement device as claimed in claim 2 characterised by: The capacitor acquisition module is used for acquiring the capacitance value of the capacitor sensor and converting the capacitance value into a digital signal. The acceleration acquisition module includes an acceleration sensor chip and is used for acquiring the axial acceleration of the piston. The memory module is a non-volatile memory and is used for temporarily storing the signals acquired by the main controller. The main controller is used for receiving the capacitance signals and the acceleration signals and storing the signals in the memory module; when the main controller receives a wireless transmission instruction, the main controller takes the data from the memory and transmits the data to the upper computer data processing module outside the cylinder. The wireless transmission module is used for transmitting data between the main controller and the upper computer data processing module. The upper computer data processing module is used for receiving and storing the skirt measurement point capacitance signals and the piston axial acceleration signals, processing the skirt measurement point capacitance signals through a parallel plate capacitor formula to obtain the oil film thickness of the measurement point, and processing the piston axial acceleration signals to determine the crankshaft angular position of each sampling point and realize the transient measurement of the crankshaft angular position and the oil film thickness. The modified piston is a piston that is adapted and improved for installing a capacitor sensor; the capacitor sensor is placed in the piston skirt, and the piston is adapted and improved by punching and grinding to install the capacitor sensor probe.

4. A piston skirt oil film thickness transient measurement device as claimed in claim 2 or 3 characterised in that: ​

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