A method and device for measuring unsprung mass

Abstract

The present invention discloses a method and device for measuring unsprung mass, wherein the method comprises the following steps: an acceleration measurement step: adding a counterweight to a wheel to be measured, and measuring acceleration time domain signals a1 and a2 of the vehicle to be measured before and after the counterweight is added, when the vehicle to be measured passes a speed reduction bump at a fixed speed at a uniform speed; a data processing step: converting the acceleration time domain signals a1 and a2 into frequency domain signals A1 and A2, respectively, and determining the frequencies f1 and f2 of the unsprung mass before and after the counterweight is added; a calculation step: calculating the unsprung mass corresponding to the wheel to be measured based on the frequencies f1 and f2 of the unsprung mass and the mass Δm of the counterweight as #imgabs0#. The advantages of the present invention are: simple and reliable measurement, simple calculation, and accurate calculation of the unsprung mass can be achieved simply and quickly, which is convenient for engineering application and research use; the application does not require disassembly of chassis parts or establishment of CAE models, and can quickly and conveniently measure the unsprung mass of a vehicle model, which facilitates the advancement of product research and development.

Description

Technical Field

[0001] The present invention relates to the technical field of automobile chassis development and testing, and in particular to a method for measuring the unsprung mass of a vehicle. Background Art

[0002] Unsprung mass is a crucial physical quantity in vehicle chassis performance development, influencing ride comfort, acceleration, and handling. While the sprung mass remains constant, reducing it to a certain extent can improve vehicle stability and passenger comfort, while also enhancing the wheel's responsiveness to the road and handling. When researching how to reduce unsprung mass, the first step is to measure it. Traditionally, unsprung mass is calculated based on the mass of chassis components: components that move with the wheels are directly weighed, and components connected to both the wheels and the body are calculated at half their mass (based on industry experience). This method, which relies on estimation and requires the removal of individual chassis components for weighing, no longer meets the evolving needs of automotive chassis development. Summary of the Invention

[0003] The object of the present invention is to overcome the deficiencies of the prior art and provide a method for measuring unsprung mass, which has accurate measurement results and is simple and reliable in calculation.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is: a method for measuring unsprung mass, comprising the following steps:

[0005] Acceleration measurement steps: Add a counterweight to the wheel to be tested, and measure the acceleration time domain signals a1 and a2 of the vehicle to be tested passing the speed bump at a fixed speed before and after adding the counterweight;

[0006] Data processing steps: Convert the acceleration time domain signals a1 and a2 into frequency domain signals A1 and A2, respectively, and determine the frequencies f1 and f2 of the unsprung mass before and after adding the counterweight.

[0007] Calculation steps: Based on the frequencies f1 and f2 of the unsprung mass and the mass Δm of the counterweight, the unsprung mass of the corresponding wheel to be tested is calculated as

[0008] Passing a speed bump at a constant speed means controlling the vehicle speed within the set speed range.

[0009] An acceleration sensor is used to measure the acceleration time domain signal corresponding to the wheel to be tested.

[0010] The acceleration sensor is arranged on the wheel center of the wheel to be tested.

[0011] The added counterweight is set on the wheel center of the wheel to be tested.

[0012] There shall be at least one speed bump.

[0013] When there are multiple speed bumps, the distance between two adjacent speed bumps is greater than a set distance threshold; the acceleration of the wheel under test before and after passing each speed bump is recorded to form an acceleration time domain signal; then, through a data processing step, the frequency of the unsprung mass corresponding to the acceleration time domain signal before and after the wheel under test passes each speed bump is obtained, and the frequencies of the multiple unsprung masses corresponding to the multiple speed bumps are averaged as the frequency of the unsprung mass of the wheel under test.

[0014] The frequency domain signal is obtained by Fourier transform, and the frequency corresponding to the maximum amplitude between 10-15 Hz is selected as the frequency of the unsprung mass.

[0015] A device for measuring unsprung mass includes an acceleration sensor, a data processing module, and a calculation module; the acceleration sensor is arranged at the wheel center of the wheel to be measured, and its output end is connected to the data processing module;

[0016] During measurement, a counterweight is placed at the center of the wheel to be tested. The vehicle then passes over a speed bump at a constant speed before and after the counterweight is added. The acceleration sensor detects the acceleration time domain signals a1 and a2 of the wheel to be tested before and after the counterweight is added, and sends them to the data processing module.

[0017] The data processing module performs Fourier transform based on the acceleration time domain signals a1 and a2 of the wheel to be tested before and after the counterweight is added, and finds the frequency corresponding to the maximum amplitude in the frequency range of 10-15 Hz as the frequency f1 and f2 of the unsprung mass of the wheel to be tested before and after the counterweight is added;

[0018] The output end of the data processing module is connected to the calculation module, and the calculation module calculates the unsprung mass m of the wheel to be tested based on the frequencies f1 and f2 of the unsprung mass transmitted by the data processing module according to the following formula:

[0019]

[0020] An output terminal of the calculation device is connected to a display device for displaying the calculated unsprung mass m.

[0021] The advantages of the present invention are: simple and reliable measurement, simple calculation, and the ability to quickly and accurately calculate the unsprung mass, making it convenient for engineering applications and research. This application does not require disassembly of chassis parts or establishment of CAE models, and can quickly and conveniently measure the unsprung mass of a vehicle model, facilitating the advancement of product research and development. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The following is a brief description of the contents and symbols in the drawings of the present invention:

[0023] Figure 1 This is a spectrum diagram of the acceleration time domain signal converted into a frequency domain signal in the present invention. DETAILED DESCRIPTION

[0024] The specific implementation of the present invention will be further explained in detail below by describing the best embodiment with reference to the accompanying drawings.

[0025] Example 1:

[0026] This embodiment provides a measurement method that can accurately and quickly measure the unsprung mass of a vehicle. The specific solution is as follows:

[0027] This measurement method includes three steps: acceleration measurement, data processing, and calculation. Since the unsprung mass is based on the wheels, the unsprung mass corresponding to the left front wheel, left rear wheel, right front wheel, and right rear wheel is respectively described. The unsprung mass corresponding to the left front wheel is used for description. The unsprung masses of the other three wheels are similar:

[0028] Acceleration Measurement: Place an accelerometer at the center of the test vehicle's left front wheel and connect it to signal processing equipment. The accelerometer can be attached to the wheel center using glue or other methods to ensure it can stably track the vehicle's motion.

[0029] The vehicle passes over a speed bump at a constant speed of V, and the acceleration signal a1 is acquired during this process. The speed V is generally a range; it is sufficient to ensure the vehicle speed remains near V. For example, the speed range can be set to fluctuate between Va and V+a, where a is the fluctuation threshold, which can be set as needed. Within this range, the vehicle speed is considered constant and meets the requirements. In this embodiment, there is only one speed bump.

[0030] Then, add a known counterweight block with a mass of Δm to the center of the left front wheel of the test vehicle. The counterweight block can be installed on it by glue or other means. Repeat the above acceleration measurement operation: pass the speed reduction bump at a fixed speed V and obtain the acceleration signal a2 during this process after the counterweight block is added.

[0031] Data processing: Perform Fourier transform on the acceleration time domain signals a1 and a2 before and after adding the counterweight to obtain the frequency domain signals A1 and A2. Find the frequency corresponding to the maximum amplitude in the range of 10 to 15 Hz, which is the frequency of the unsprung mass. Figure 1As shown in the figure, it is a schematic diagram of the spectrum after the driving time domain signal is converted into a frequency domain signal. In the figure, the circled value is the value with the maximum amplitude in the range of 10-15Hz, and its corresponding frequency is 11.5Hz. At this time, 11.5Hz is considered to be the frequency of the unsprung mass of the wheel. In this way, the acceleration time domain signals a1 and a2 can be processed to obtain the unsprung mass frequency f1 before the addition of the counterweight and the unsprung mass frequency f2 after the addition of the counterweight, respectively.

[0032] Calculation steps: Calculate the frequency before weighting as f1, the frequency after weighting as f2, and the mass of the weight block as Δm. Then the original unsprung mass of the left front wheel is

[0033] The above example uses the left front wheel's unsprung mass measurement as an example. The methods for the right front / left rear / right rear are similar, except that counterweights are added to the right front / left rear / right rear wheels to calculate the corresponding unsprung masses.

[0034] The key points of this embodiment include:

[0035] (1) Sensor layout: fix the acceleration sensor near the wheel center of the left front steering knuckle and connect it to the signal processing host;

[0036] (2) The driver passes the speed bump at a constant speed and collects the acceleration signal;

[0037] (3) Add a counterweight of known mass to the left front wheel hub to ensure a reliable connection;

[0038] (4) The driver again drives across the speed bump at a constant speed and collects acceleration signals;

[0039] (5) The data is processed to obtain the unsprung frequencies twice, and the unsprung mass of the original vehicle is calculated through the formula.

[0040] The present application also provides a device for measuring unsprung mass, which includes hardware components for measuring unsprung mass, including an acceleration sensor, a data processing module, and a calculation module; wherein the acceleration sensor is arranged at the wheel center of the wheel to be measured, and its output end is connected to the data processing module;

[0041] During measurement, a counterweight is placed at the center of the wheel to be tested. The vehicle then passes over a speed bump at a constant speed before and after the counterweight is added. The acceleration sensor detects the acceleration time domain signals a1 and a2 of the wheel to be tested before and after the counterweight is added, and sends them to the data processing module.

[0042] The data processing module performs Fourier transform on the acceleration time domain signals a1 and a2 of the test wheel before and after the counterweight is added, and finds the frequency corresponding to the maximum amplitude in the frequency range of 10-15 Hz as the frequency f1 and f2 of the unsprung mass of the test wheel before and after the counterweight is added;

[0043] The output end of the data processing module is connected to the calculation module, which calculates the unsprung mass m of the wheel to be tested based on the frequencies f1 and f2 of the unsprung mass transmitted by the data processing module according to the following formula:

[0044]

[0045] The output end of the calculation device is connected to a display device for displaying the calculated unsprung mass M. The data processing module and the calculation module can be integrated into a host or controller capable of data processing and calculation.

[0046] The principle of the unsprung mass calculation formula is deduced as follows:

[0047] From the automobile theory we know

[0048] Frequency of unsprung mass

[0049]

[0050] Where m is the unsprung mass, k is the suspension stiffness, and kt is the tire stiffness.

[0051] In step 1, when the unsprung mass is m1,

[0052]

[0053] When the unsprung mass is m2=m1+Δm,

[0054]

[0055] By simplifying the above two formulas, we can get:

[0056]

[0057] After further simplification

[0058]

[0059] The automotive theory includes:

[0060] For the vibration of the dual-mass undamped system of a car, its differential equation of motion is:

[0061]

[0062] Among them, m2 is the suspension mass, m1 is the unsprung mass, z2 is the wheel displacement, z1 is the body displacement, k is the suspension stiffness, k t is the tire stiffness.

[0063] If m2 is stationary (z2=0), it is equivalent to the unsprung mass m1 vibrating freely with a single degree of freedom and no damping, so we can get

[0064]

[0065] Solving the equation, we can get

[0066]

[0067] p t is the natural circular frequency of the unsprung mass, and we can further obtain

[0068] f t Unsprung frequency deviation

[0069] Example 2:

[0070] This embodiment will calculate the unsprung mass using two speed bumps. The specific solution is as follows:

[0071] Acceleration Measurement: Place an accelerometer at the center of the test vehicle's left front wheel and connect it to signal processing equipment. The accelerometer can be attached to the wheel center using glue or other methods to ensure it can stably track the vehicle's motion.

[0072] The speed bump can be a bump set on the road in the form of a speed strip or other method to achieve the deceleration function. This application takes two speed bumps as an example for explanation. Two speed bumps are set in the direction of wheel travel. The vertical distance between the two speed bumps must be greater than the set distance threshold, because it is necessary to ensure that the wheel has completely passed through one of the speed bumps before entering the next speed bump, avoiding inaccurate measurements caused by the wheel traveling between the two speed bumps. In this way, it can be ensured that the vehicle passes through the next speed bump after passing one speed bump, thus forming two processes of passing the speed bumps.

[0073] Similarly, in this embodiment, the vehicle passes through two speed bumps at a constant speed of V. Since the vehicle passes through two speed bumps, this process can actually be decomposed into two speed bump passes, with each speed bump being considered as a completed speed bump pass. The acceleration time domain signals acquired during this process include two time domain signals a11 and a12. These two signals are the acceleration time domain signals corresponding to the left front wheel when no counterweight is added. The vehicle speed V is generally a range value here. As long as the vehicle speed is kept near V, for example, the speed range can be set to fluctuate between Va and V+a. a is the fluctuation threshold, which can be set as needed. Within this range, the vehicle speed is considered fixed and meets the requirements. A11 is the acceleration signal collected during the first speed bump pass, and a12 is the acceleration signal corresponding to the second speed bump pass.

[0074] Then, add a known counterweight block at the center of the left front wheel of the test vehicle, whose mass is measured as Δm, where the counterweight block can be installed on it by glue or other means; repeat the above acceleration measurement operation: pass the speed reduction bump at a fixed vehicle speed V, and obtain the acceleration signals a21 and a22 during this process after the counterweight block is added. a21 and a22 are the acceleration signals collected during the first speed reduction bump process, and a22 is the acceleration signal corresponding to passing the second speed reduction bump.

[0075] Data Processing: Fourier transform the acceleration time-domain signals a1 and a2 before and after the counterweight is added to obtain frequency-domain signals. The frequency corresponding to the maximum amplitude in the 10-15 Hz range is identified as the frequency of the unsprung mass. Fourier transform the two time-domain signals a11 and a12 before the counterweight is added, respectively, to obtain frequency-domain spectrograms T11 and T12 corresponding to a11 and a12. The unsprung mass frequencies f11 and f12 are then found in spectrograms T11 and T12, respectively. The frequency of the unsprung mass before the counterweight is added is then averaged to obtain f1 = (f11 + f12) / 2.

[0076] Similarly, perform Fourier transform on the two time domain signals a21 and a22 after adding the counterweight, and obtain the frequency domain spectrum diagram T21 corresponding to a21 and the frequency domain spectrum diagram T22 corresponding to a22. Then, find the frequency f21 of the unsprung mass in the spectrum diagram T21, and find the frequency f22 of the unsprung mass in the spectrum diagram T22. Then, take the average to obtain the frequency f2 of the unsprung mass before adding the counterweight, which is (f21 + f22) / 2.

[0077] Calculation steps: Calculate the frequency before weighting as f1, the frequency after weighting as f2, and the mass of the weight block as Δm. Then the original unsprung mass of the left front wheel is

[0078] The above example uses the left front wheel's unsprung mass measurement as an example. The methods for the right front / left rear / right rear are similar, except that counterweights are added to the right front / left rear / right rear wheels to calculate the corresponding unsprung masses.

[0079] This application is illustrated using two speed bumps as an example, but multiple speed bumps can actually be used to increase the accuracy of the calculation. When there are multiple speed bumps, the distance between two adjacent speed bumps is greater than a set distance threshold; the acceleration of the wheel to be tested before and after passing each speed bump is recorded to form an acceleration time domain signal; then, through a data processing step, the frequency of the unsprung mass corresponding to the acceleration time domain signal before and after the wheel to be tested passes each speed bump is obtained, and then the frequencies of the multiple unsprung masses corresponding to the multiple speed bumps are averaged as the frequency of the unsprung mass of the wheel to be tested.

[0080] Obviously, the specific implementation of the present invention is not limited to the above-mentioned methods. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention, they are all within the scope of protection of the present invention.

Claims

1. A method for measuring unsprung mass, characterized by: The steps include: Acceleration measurement steps: Add a counterweight to the wheel to be tested, and measure the acceleration time domain signals a1 and a2 of the vehicle to be tested passing the speed bump at a fixed speed before and after adding the counterweight; Data processing steps: Convert the acceleration time domain signals a1 and a2 into frequency domain signals A1 and A2, respectively, and determine the frequencies f1 and f2 of the unsprung mass before and after adding the counterweight. The frequency domain signal is obtained by Fourier transform, and the frequency corresponding to the maximum amplitude between 10-15 Hz is selected as the frequency of the unsprung mass; Calculation steps: Based on the frequencies f1 and f2 of the unsprung mass and the mass Δm of the counterweight, the unsprung mass of the wheel to be tested is calculated as 2. The method for measuring unsprung mass according to claim 1, wherein: Passing a speed bump at a constant speed means controlling the vehicle speed within the set speed range.

3. The method for measuring unsprung mass according to claim 1, wherein: An acceleration sensor is used to measure the acceleration time domain signal corresponding to the wheel to be tested.

4. The method for measuring unsprung mass according to claim 3, wherein: The acceleration sensor is arranged on the wheel center of the wheel to be tested.

5. The method for measuring unsprung mass according to claim 1, wherein: The added counterweight is set on the wheel to be tested.

6. The method for measuring unsprung mass according to claim 1, wherein: There shall be at least one speed bump.

7. The method for measuring unsprung mass according to claim 6, wherein: When there are multiple speed bumps, the distance between two adjacent speed bumps is greater than a set distance threshold; the acceleration of the wheel under test before and after passing each speed bump is recorded to form an acceleration time domain signal; then, through a data processing step, the frequency of the unsprung mass corresponding to the acceleration time domain signal before and after the wheel under test passes each speed bump is obtained, and the frequencies of the multiple unsprung masses corresponding to the multiple speed bumps are averaged as the frequency of the unsprung mass of the wheel under test.

8. A device for measuring unsprung mass, characterized by: It includes an acceleration sensor, a data processing module, and a calculation module; the acceleration sensor is arranged at the wheel center of the wheel to be tested, and its output end is connected to the data processing module; During measurement, a counterweight is placed at the center of the wheel to be tested. The vehicle then passes over a speed bump at a constant speed before and after the counterweight is added. The acceleration sensor detects the acceleration time domain signals a1 and a2 of the wheel to be tested before and after the counterweight is added, and sends them to the data processing module. The data processing module performs Fourier transform based on the acceleration time domain signals a1 and a2 of the wheel to be tested before and after the counterweight is added, and finds the frequency corresponding to the maximum amplitude in the frequency range of 10-15 Hz as the frequency f1 and f2 of the unsprung mass of the wheel to be tested before and after the counterweight is added; The output end of the data processing module is connected to the calculation module, and the calculation module calculates the unsprung mass m of the wheel to be tested based on the frequencies f1 and f2 of the unsprung mass transmitted by the data processing module according to the following formula: Where Δm is the mass of the counterweight.

9. The unsprung mass measuring device according to claim 8, characterized in that: The output end of the calculation module is connected to a display device for displaying the calculated unsprung mass m.

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