CN107941488B - Method for measuring dynamic stiffness of vehicle leaf spring - Google Patents
Method for measuring dynamic stiffness of vehicle leaf spring Download PDFInfo
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- CN107941488B CN107941488B CN201711156386.5A CN201711156386A CN107941488B CN 107941488 B CN107941488 B CN 107941488B CN 201711156386 A CN201711156386 A CN 201711156386A CN 107941488 B CN107941488 B CN 107941488B
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Abstract
The invention relates to a method for measuring the dynamic stiffness of a vehicle leaf spring, which belongs to the technical field of automobile suspensions.
Description
Technical Field
The invention relates to a method for measuring the dynamic stiffness of a vehicle steel plate spring, and belongs to the technical field of automobile suspensions.
Background
The steel plate spring is an elastic element in the automobile suspension, and is widely applied to commercial vehicles due to the characteristics of simple structure, convenient maintenance, low manufacturing cost, capability of being used as a guide mechanism and the like. In a steel plate spring suspension system, sprung resonance frequency and absorber parameters based on the matching are important factors influencing vehicle smoothness, wherein the sprung resonance frequency is influenced by dynamic stiffness of a steel plate spring, but the sprung resonance frequency is influenced by friction, the dynamic stiffness of the steel plate spring is often larger than the design stiffness when the vehicle runs, and particularly, the dynamic stiffness of a multi-leaf spring vehicle type or a few-leaf spring vehicle type with poor lubrication can be multiple times of the design stiffness, so that if the suspension system is subjected to dynamic characteristic design based on the design stiffness of the steel plate spring, larger deviation can occur, and finally the vehicle smoothness is poor.
At present, scholars at home and abroad study the influence of friction of the steel plate springs through experiments, and point out that the axial load and the amplitude are factors influencing the dynamic stiffness, and the dynamic stiffness of the same steel plate spring can be different under different axial loads, road surface excitation and tire excitation. Therefore, if the dynamic characteristics of the suspension system are predicted through the design rigidity measured by the loading and unloading curves of the rack, larger deviation can be caused due to the influence of friction; or, the dynamic stiffness of the spring is measured by simulating the resonance working condition on the spring through the rack, so that the test process is complicated and long in period, and the steel plate spring needs to be disassembled in the test process, thereby wasting time and labor. Therefore, how to obtain the dynamic stiffness of the leaf spring at the time of sprung resonance is an urgent problem to be solved in designing the dynamic characteristics of the suspension system.
Disclosure of Invention
In order to solve the technical defects, the invention provides a method for measuring the dynamic stiffness of the steel plate spring of the vehicle, which measures the resonance frequency on the spring through the running condition of the vehicle, reversely calculates the dynamic stiffness of the steel plate spring based on the resonance frequency on the spring, the mass under the spring and the mass on the spring, the stiffness of a tire and other parameters, and can accurately and efficiently measure the dynamic stiffness of the steel plate spring during the resonance on the spring.
The technical scheme of the invention is as follows: a method for measuring the dynamic stiffness of a vehicle leaf spring mainly comprises the following steps:
step one, arranging acceleration sensors at a vehicle bridge under a spring and a vehicle frame on the spring, and driving a vehicle into a test road;
step two, carrying out a driving condition test, carrying out frequency domain transformation on an acceleration signal measured by an acceleration sensor, identifying the sprung resonance phenomenon based on a frequency spectrum, and recording sprung resonance frequency fi;
step three, calculating to obtain the dynamic stiffness k of the steel plate spring during the sprung resonance according to the sprung resonance frequency fi, the unsprung mass m1, the sprung mass m2 and the tire stiffness Kt, wherein the calculation formula is as follows,
the technical scheme of the invention also comprises: the resonance frequency on the spring in the three steps is calculated by taking the average value and is recorded as the average resonance frequency fe, the calculation formula of the dynamic stiffness k of the steel plate spring during the resonance on the spring is as follows,
the technical scheme of the invention also comprises: the average resonance frequency fe is obtained by,
firstly, when a vehicle is tested under a driving condition, recognizing the sprung resonance phenomenon based on a frequency spectrum, and recording a rotating speed characteristic parameter when the sprung resonance occurs;
secondly, performing N-round constant speed tests based on the rotating speed characteristic parameters, wherein N takes a value of 2-100, and recording the sprung resonance frequency of each round of tests as fi, wherein i is 1, 2, 3 … and N;
thirdly, averaging the resonance frequencies of the N springs to obtain an average resonance frequency
The technical scheme of the invention also comprises: and the test road tested at the constant speed in the second step is the same road section in the same direction.
The technical scheme of the invention also comprises: the rotating speed characteristic parameter in the first step is one of a vehicle speed, an engine rotating speed in a certain gear and a rotating speed of a transmission shaft in a certain gear.
The technical scheme of the invention also comprises: and in the first step, the measuring direction of the acceleration sensor is vertical to the ground.
The technical scheme of the invention also comprises: and the driving working condition in the step two is one of an acceleration working condition and a sliding working condition.
The technical scheme of the invention also comprises: and in the second step, when the amplitude-frequency values of the measured values of the acceleration sensors arranged on the unsprung vehicle axle part and the sprung vehicle frame part after frequency domain transformation simultaneously have local maximum values at the same frequency, the sprung amplitude is greater than the unsprung amplitude, and the phase-frequency values are equal at the same frequency, the sprung resonance phenomenon can be identified, and the same frequency is recorded as sprung resonance frequency fi.
The technical scheme of the invention also comprises: the test road in the first step is a straight section of a high-grade highway.
The invention has the beneficial effects that: the method is used for measuring the dynamic stiffness of the steel plate spring based on the sprung resonance working condition, the acceleration sensor is arranged at the position of the unsprung axle and the sprung frame, the sprung resonance frequency is measured by using the vehicle running working condition, then the dynamic stiffness of the steel plate spring is reversely obtained based on the sprung resonance frequency, the unsprung mass, the sprung mass, the tire stiffness and other parameters, the influence effect of friction on the dynamic stiffness is reflected in the test result, the method is more accurate compared with the method for measuring the stiffness by loading and unloading tests, and the dynamic stiffness of the steel plate spring can be more efficiently measured without disassembling the steel plate spring and bench tests.
Drawings
FIG. 1 is a flowchart of the measurement method of the present invention.
Detailed Description
The invention is further illustrated by the following examples in conjunction with the accompanying drawings.
According to the method for measuring the dynamic stiffness of the steel plate spring of the vehicle, the acceleration sensors are arranged at the positions of the unsprung axle and the sprung axle, the sprung resonance frequency is measured according to the running condition of the vehicle, the dynamic stiffness of the steel plate spring is reversely solved based on the sprung resonance frequency, the unsprung mass, the sprung mass, the tire stiffness and other parameters, the dynamic stiffness of the steel plate spring during the sprung resonance can be quickly and accurately measured, and guidance and verification are conducted on the design of the steel plate spring.
The first embodiment of the invention:
take a leaf spring suspension system as an example for the front suspension of a truck.
Wherein, the unsprung mass m1 is 369.61kg, the sprung mass m2 is 1675.39kg, and the total rigidity kt of the tires on both sides is 960N/mm. The determination steps are as follows:
the method comprises the following steps: one-way acceleration sensors are arranged at the positions of the front suspension spring lower axle and the spring upper frame, and the measuring direction of the acceleration sensors is vertical to the ground, so that whether resonance occurs or not can be judged by using the change of vertical data. A straight section of a certain high-grade highway in a suburb is selected as a test road, namely, a road section without turning or slope is selected as much as possible for testing. In order to improve the accuracy of measured data and reduce the adverse effect of external test conditions on the measured data, the selected test road conditions can be controlled to be that the gradient of the road surface is less than 1%, the unevenness is uniform and has no sudden change, and the road surface is dry during the test.
Step two: the test is carried out by adopting an acceleration working condition, when the rotating speed of the 4-gear transmission shaft is about 960rpm, amplitude-frequency values of the axle measuring points and the frame measuring points in the direction vertical to the ground have local peak values, the frame measuring points are larger than the axle measuring points, phase-frequency values are equal, the phase-frequency values are in a front suspension spring upper resonance state, and the corresponding frequency fi is 2.870Hz, namely the spring upper resonance frequency.
Step three: the sprung resonance frequency fi is 2.870Hz, the unsprung mass m1 is 369.61kg, the sprung mass m2 is 1675.39kg, and the total tire stiffness kt is 960N/mm, which are substituted into the calculation formula:
and reversely solving the dynamic stiffness k of the single-side steel plate spring, namely 776N/mm.
In the second embodiment of the invention, the selected suspension system is the same as the first embodiment, but the difference is that the resonance frequency is subjected to multiple tests and the average value is calculated so as to improve the accuracy of the measurement result. As shown in FIG. 1, the specific measurement procedure is as follows:
the method comprises the following steps: the method is characterized in that one-way acceleration sensors are arranged at the positions of a front suspension spring lower axle and a spring upper axle, a straight section of a certain high-grade highway in a suburb is selected as a test road, the gradient of the road surface is less than 1%, unevenness is uniform and has no sudden change, and the road surface is dry during testing.
Step two: the rotating speed of a transmission shaft at the 4-gear is taken as a characteristic parameter, an acceleration condition is adopted for testing, when the rotating speed of the 4-gear transmission shaft is about 960rpm, amplitude frequency values of an axle measuring point and a frame measuring point in the direction vertical to the ground have local peak values, the frame measuring point is larger than the axle measuring point, phase frequency values are equal, and the state is a resonance state on a front suspension spring.
Step three: keeping the operating condition of 960rpm of the 4-gear transmission shaft of the vehicle to perform 10 groups of constant speed tests, wherein each round of tests are performed on the same road section in the same direction so as to ensure the accuracy of the measured data. Based on frequency spectrum, sprung resonance frequency f 1-2.872 Hz, f 2-2.876 Hz, f 3-2.889 Hz, f 4-2.884 Hz, f 5-2.875 Hz, f 6-2.864 Hz, f 7-2.867 Hz, f 8-2.879 Hz, f 9-2.866 Hz, and f 10-2.891 Hz are identified.
Step four: the 10 sprung resonance frequencies are substituted into the calculation:
the average resonance frequency fe is calculated to be 2.876 Hz.
Step five: the average resonance frequency fe is 2.876Hz, the unsprung mass m1 is 369.61kg, the sprung mass m2 is 1675.39kg, and the total tire stiffness kt is 960N/mm, which are substituted into the calculation formula:
and the dynamic stiffness k of the unilateral steel plate spring is back-solved to 786N/mm.
The above description is only exemplary of the present invention and should not be taken as limiting the invention in any way, and any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (6)
1. A method for measuring the dynamic stiffness of a vehicle leaf spring mainly comprises the following steps:
step one, arranging acceleration sensors at the bridge part of the unsprung vehicle and the sprung vehicle frame part right above the bridge part, and driving the vehicle into a test road;
step two, testing the driving condition, carrying out frequency domain transformation on the acceleration signal measured by the acceleration sensor, identifying the resonance phenomenon on the spring based on the frequency spectrum, and recording the resonance frequency f on the springi；
Step three, according to the resonance frequency f on the springiUnsprung mass m1Sprung mass m2And overall tire stiffness KtCalculating the dynamic stiffness k of the steel plate spring when the sprung resonance is obtained by the following calculation formula,
the measuring direction of the acceleration sensor in the first step is vertical to the ground;
the driving working condition in the second step is one of an acceleration working condition and a sliding working condition;
the test road in the first step is a straight section of a high-grade highway.
2. The method for determining the dynamic stiffness of a leaf spring of a vehicle according to claim 1, wherein: the resonance frequency on the spring in the third step is calculated by taking the average value and is recorded as the average resonance frequency feThe calculation formula of the dynamic stiffness k of the steel plate spring during the sprung resonance is as follows,
3. the method for determining the dynamic stiffness of a leaf spring of a vehicle according to claim 2, wherein: the average resonance frequency feThe method for obtaining the content of the Chinese character 'Gangsu',
firstly, when a vehicle is tested under a driving condition, recognizing the sprung resonance phenomenon based on a frequency spectrum, and recording a rotating speed characteristic parameter when the sprung resonance occurs;
secondly, performing N rounds of constant speed tests based on the rotating speed characteristic parameters, wherein N takes a value of 2-100, and recording the sprung resonance frequency f of each round of testsiWherein i ═ 1, 2, 3 …, N;
thirdly, averaging the resonance frequencies of the N springs to obtain an average resonance frequency
4. A method of determining the dynamic stiffness of a vehicle leaf spring as set forth in claim 3, wherein: and the test road tested at the constant speed in the second step is the same road section in the same direction.
5. A method of determining the dynamic stiffness of a vehicle leaf spring as set forth in claim 3, wherein: the rotating speed characteristic parameter in the first step is one of a vehicle speed, an engine rotating speed in a certain gear and a rotating speed of a transmission shaft in a certain gear.
6. The method for determining the dynamic stiffness of a leaf spring of a vehicle according to claim 1, wherein: in the second step, when the amplitude-frequency values of the measured values of the acceleration sensors arranged on the unsprung vehicle axle part and the sprung vehicle frame part after frequency domain transformation simultaneously have local maximum values at the same frequency, the sprung amplitude is greater than the unsprung amplitude, and the phase-frequency values are equal at the same frequency, the phenomenon of sprung resonance can be identified, and the phenomenon of sprung resonance can be identifiedA frequency recorded as the sprung resonant frequency fi。
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