A method for controlling low-frequency road noise inside an automobile based on active control

Abstract

The present invention provides a method for controlling low-frequency road noise inside an automobile. By modifying the transfer function of the vehicle body, when the vehicle body is subjected to external excitation, the vibration amplitude of the vehicle body is at a relatively low level. The resonance frequency of the vehicle body is modified by the feedback force applied by the actuator to avoid the overlap between the resonance frequency of the vehicle body and the resonance frequency of the acoustic cavity inside the vehicle. Without making major modifications to the automobile body, the vibration and sound radiation of the vehicle body caused by external excitation can be effectively reduced, and the coupled resonance between the vehicle body and the acoustic cavity inside the vehicle can be avoided.

Description

Technical Field

[0001] The present invention relates to automotive NVH, and specifically to a method for controlling low-frequency road noise inside an automobile. Background Art

[0002] The control of low-frequency road noise inside an automobile is a technical challenge in automotive NVH control. Among them, the low-frequency drumming sound is a typical case of low-frequency road noise inside an automobile. The mechanism of low-frequency drumming in an automobile is mainly the acoustic-vibration coupling phenomenon generated between the automobile body and the acoustic cavity inside the vehicle. The excitation from the road surface is transmitted through the automobile tire-suspension system-body, causing low-frequency vibration of the body and radiating low-frequency noise similar to drumming sound into the vehicle. If the road surface excitation frequency is close to the body resonance frequency, the drumming sound inside the vehicle will be further amplified, causing an uncomfortable ear-pressing feeling for passengers. Currently, the common methods for controlling low-frequency drumming in an automobile include: Method 1, adding a mass block or stiffness to the body to modify the vibration characteristics of the body; Method 2, installing a vibration absorber on the body to dissipate vibration energy, etc. However, in Method 1, adding a mass block to the body is not conducive to vehicle lightweighting, and increasing the stiffness by welding stiffeners to the body and other methods requires significant modification to the body. In Method 2, installing a vibration absorber on the body requires a certain installation space, and the installation of a vibration absorber is usually restricted by the automotive structural design.

[0003] Therefore, based on the existing control methods, it is necessary to design a new method for controlling low-frequency road noise in an automobile, that is, a method for controlling low-frequency drumming sound. Summary of the Invention

[0004] Aiming at the problems existing in the existing control methods, the present invention provides a method for controlling low-frequency road noise inside an automobile, aiming to effectively reduce the body vibration and sound radiation caused by external excitation without significant modification to the automobile body, and avoid the coupled resonance between the body and the acoustic cavity inside the vehicle.

[0005] The technical solution of the present invention is as follows:

[0006] The basic principle on which the method for controlling low-frequency road noise inside an automobile proposed by the present invention is based is: the response characteristics (i.e., transfer function) of a system are related to the characteristic frequency of the system, and the response characteristics of the system can be changed by modifying the characteristic frequency of the system through an active control method.

[0007] Hereinafter, the theoretical principle and derivation process of the method for controlling low-frequency road noise inside an automobile according to the present invention will be described as follows:

[0008] The body of a dynamic automobile is considered as a dynamic system with a mass of M, a damping of C, and a stiffness of K, which is subjected to an external excitation F, and its vibration control equation is

[0009]

[0010] where u is the additional force applied by the actuator.

[0011]

[0012] where b is the distribution position of the actuator, g and f are the gains corresponding to the vibration displacement response and vibration velocity response of the vehicle body, x(t) is the measured vibration displacement of the vehicle body, and is the measured vibration velocity of the vehicle body; T is the transpose symbol.

[0013] Combining Equation (1) and (2) and performing Laplace transform, the new transfer function of the vehicle body is obtained

[0014]

[0015] Before applying control, the transfer function of the vehicle body is

[0016] H(s) = (Ms 2 + Cs + K) -1 (4)

[0017] Comparing Equation (3) with (4), it can be seen that the equivalent damping of the vehicle body after applying control becomes C + bf T , and the equivalent stiffness of the vehicle body becomes K + bgT. Expressing the transfer function of the vehicle body after applying control in terms of the transfer function H(s) before applying control, we can obtain

[0018]

[0019] By solving 1 + (g + sf) T H(s)b = 0, the resonance frequency μ of the vehicle body after applying control can be obtained. If the transfer function H(s) of the vehicle body before applying control is known, by setting the actuator position vector b and the resonance frequency {μ1 μ2 ··· μ 2n} of the vehicle body after applying control, the gains g and f corresponding to the vibration displacement and vibration velocity of the vehicle body can be obtained.

[0020] The above relationship satisfies

[0021] (g + μ k f) T H(μ k )b = -1, k = 1, 2, ···, 2n (6)

[0022] Define r k = H(μ k )b to obtain

[0023]

[0024] By inverting the G matrix, the gains g and f corresponding to the vehicle body vibration displacement and the vehicle body vibration velocity can be obtained. Using this control method, the transfer function of the vehicle body can be modified to achieve the purpose of reducing the vehicle body vibration and the interior noise.

[0025] In practice, when the external excitation is close to the natural frequency of the vehicle body, the vibration amplitude of the vehicle body will increase significantly, thereby causing obvious interior noise. Based on the above theoretical principles, the present invention proposes an active control method. By modifying the transfer function of the vehicle body, when the vehicle body is subjected to external excitation, the vibration amplitude of the vehicle body is at a low level. In addition, the resonance frequency of the vehicle body is modified by the feedback force applied by the actuator to avoid the overlap of the resonance frequency of the vehicle body and the resonance frequency of the interior acoustic cavity. The purpose of reducing the low-frequency road noise in the vehicle is achieved through the above adjustment.

[0026] Specifically, the method for controlling the low-frequency road noise in the vehicle proposed by the present invention mainly includes the following steps:

[0027] Step 1, arrange vibration sensors at the key parts of the vehicle body that cause low-frequency road noise in the vehicle for static testing: randomly apply excitation to the vehicle, and measure and obtain the vibration signals at the positions of the vibration sensors arranged on the vehicle body.

[0028] Step 2, use the vibration signal spectrum measured at the measurement points arranged on the vehicle body to obtain the transfer function H(s) of the vehicle body, and analyze the resonance frequency of the vehicle body.

[0029] Step 3, adjust the resonance frequency of the vehicle body according to the frequency avoidance principle that the difference between the resonance frequency of the vehicle body and the resonance frequency of the interior acoustic cavity is not less than 2 Hz; calculate the gains g and f corresponding to the vehicle body vibration displacement and the vehicle body vibration velocity according to the adjustment amplitude of the resonance frequency of the vehicle body and the transfer function of the vehicle body.

[0030] Step 4, when the vehicle is in operation, measure and obtain the vibration displacement and vibration velocity signals at the positions of the sensors on the vehicle body. Calculate the control force that needs to be applied to the vehicle body by multiplying the vehicle body vibration displacement and the vehicle body vibration velocity by their respective corresponding gains:

[0031]

[0032] where x(t) is the measured vehicle body vibration displacement, is the measured vehicle body vibration velocity; T is the transpose symbol.

[0033] Step 5, install an actuator at the key parts of the vehicle body, and apply a feedback control force Fc = bu(t) to the vehicle body to achieve the purpose of modifying the transfer function of the vehicle body and further controlling the low-frequency road noise in the vehicle, where b is the position vector of the feedback force.

[0034] According to an embodiment of the present invention, step 2 is based on the spectrum H(ω) of the measured vehicle body vibration signal, where ω is the frequency, and performs a Laplace transform s = jω on it. The transfer function of the vehicle body is obtained as H(s).

[0035] Further, the specific calculation of the gains g and f corresponding to the vehicle body vibration displacement and the vehicle body vibration velocity according to the adjustment amplitude of the vehicle body resonance frequency and the transfer function of the vehicle body is as follows: Analyze the resonance frequency of the vehicle body using the measured vehicle body vibration signal; when the external excitation frequency is close to this resonance frequency, the vibration amplitude of the vehicle body is amplified. Therefore, the vehicle body resonance frequency is the pole of the vehicle body transfer function. By increasing the method of active feedback control, the original resonance frequency of the vehicle body is replaced with a new frequency, thereby modifying the transfer function of the vehicle body, and then calculating the corresponding gains g and f.

[0036] Further, modifying the transfer function of the vehicle body is to modify the original transfer function H(s) of the vehicle body into a new transfer function of the vehicle body:

[0037]

[0038] b is the distribution position of the actuator, g and f are the gains corresponding to the vibration displacement response and the vibration velocity response at the vehicle body measurement point position, H(s) is the vehicle body transfer function before applying control, is the vehicle body transfer function after applying control, s = jω, ω is the frequency.

[0039] According to an embodiment of the present invention, the system gains g and f are calculated according to the following formula:

[0040] (g + μ k f) T H(μ k )b = -1, k = 1, 2,..., 2n

[0041] Define r k = H(μ k )b to obtain

[0042]

[0043] By inverting the G matrix, the gains g and f corresponding to the vibration displacement response and the vibration velocity response at the sensor position on the vehicle body can be obtained.

[0044] In an embodiment of the present invention, the actuator is a piezoelectric stack actuator that can be directly purchased on the market. Excitation from the tire and the road surface usually causes the vibration of the car tailgate and resonance with the acoustic cavity inside the car, resulting in low-frequency road noise inside the car. The piezoelectric stack actuator can be directly bonded to the car tailgate with high-strength glue for experiments without modifying the original structure of the car.

[0045] The present invention has the following advantages:

[0046] 1. By modifying the transfer function of the vehicle body, when the vehicle body is excited by the outside world, the vibration amplitude of the vehicle body is at a relatively low level, effectively reducing the vibration and sound radiation of the vehicle body caused by the outside excitation, and avoiding the coupling resonance between the vehicle body and the acoustic cavity inside the car.

[0047] 2. Compared with the traditional method, this method can effectively reduce the low-frequency knocking sound of the car with little modification to the car.

[0048] 3. The implementation process of this method is simple and easy to achieve.

[0049] 4. This method has control effects on both the vibration of the car body and the noise inside the car, and can control multiple resonance frequencies of the vehicle body simultaneously, or selectively control a specific resonance frequency of the vehicle body. Description of the Drawings

[0050] Figure 1 It is a simplified coupling model of the car body and the cavity inside the car used in an embodiment of the present invention.

[0051] Figure 2 It is a schematic diagram of controlling the low-frequency road noise inside the car established in an embodiment of the present invention.

[0052] Figure 3 It is a schematic diagram of using a single actuator to control the first two modes in an embodiment of the present invention.

[0053] Figure 4 Control effect of using a single actuator to control the first two modes in an embodiment of the present invention. (a) Structural vibration, (b) Sound pressure inside the car.

[0054] Figure 5 It is a schematic diagram of using two actuators to control the first four modes in an embodiment of the present invention.

[0055] Figure 6 Control effect of using two actuators to control the first four modes in an embodiment of the present invention. (a) Structural vibration, (b) Sound pressure inside the car. Detailed Embodiments

[0056] The following further describes the operation arrangement and control effect of this method in controlling the low-frequency road noise inside the car with reference to the drawings.

[0057] As Figure 2 shown, implementing the method of the present invention requires hardware and a control algorithm. The hardware part includes several vibration sensors and actuators. The vibration sensors are used to measure the vibration displacement and vibration speed of the vehicle body, and the actuators are used to output a control force to the vehicle body. The installation positions of the vibration sensors and actuators are determined according to the resonance frequency of the vehicle body to be controlled. Generally speaking, it should be avoided to arrange the sensors and actuators at the nodes of the vehicle body mode corresponding to the resonance frequency to be controlled. The control algorithm calculates the control force of each actuator based on the measured vibration displacement and vibration speed of the vehicle body and their respective gains, and the actuators apply the control force to the vehicle body, ultimately achieving the purpose of controlling the vibration and noise of the vehicle body.

[0058] As Figure 1 shown, in the following embodiments, the coupling effect between the vehicle body and the interior acoustic cavity is simplified to the coupling between an elastic plate and an acoustic cavity. The elastic plate simulates the vehicle body, and the acoustic cavity simulates the interior acoustic environment.

[0059] The specific implementation process of controlling the low-frequency road noise inside the vehicle includes:

[0060] First, vibration sensors are arranged at the key parts of the vehicle body that cause low-frequency road noise inside the vehicle to measure the vibration acceleration signal at the positions of the sensors on the vehicle body By integrating the vibration acceleration signal with respect to time, the vibration speed response at the positions of the sensors on the vehicle body is obtained and the vibration displacement response x(t).

[0061] For example, as Figure 3 shown, the displacement and speed responses at positions s1 and s2 on the elastic plate are measured by 2 vibration sensors, or Figure 4 shown, the displacement and speed responses at positions s1, s2, s3, and s4 on the elastic plate are measured by 4 vibration sensors.

[0062] The transfer function test of the vehicle body is carried out offline. An external excitation is randomly applied to the vehicle body, and the vibration displacement response spectrum H(ω) of the vehicle body is measured, where ω is the frequency. Performing the Laplace transform s = jω on it, the transfer function of the vehicle body is obtained as H(s).

[0063] Then, the gains g and f corresponding to the vibration displacement and vibration speed of the vehicle body are calculated offline according to the control target.

[0064] Here, it is necessary to use the active control method based on pole replacement to modify the original resonance frequency of the vehicle body, and then calculate the corresponding gains g and f in this control method.

[0065] Adjust the resonance frequency of the vehicle body according to the principle of frequency avoidance where the difference between the resonance frequency of the vehicle body and the resonance frequency of the vehicle interior acoustic cavity is not less than 2 Hz. Calculate the gains g and f corresponding to the vehicle body vibration displacement and vehicle body vibration speed based on the adjustment amplitude of the vehicle body resonance frequency and the transfer function of the vehicle body. Specifically: Analyze the resonance frequency of the vehicle body using the measured vehicle body vibration signal; when the external excitation frequency is close to this resonance frequency, the vibration amplitude of the vehicle body is amplified. Therefore, the vehicle body resonance frequency is the pole of the vehicle body transfer function. Replace the original resonance frequency of the vehicle body with a new frequency by adding an active feedback control method, thereby modifying the transfer function of the vehicle body, and then calculate the corresponding gains g and f.

[0066] Here, modifying the original resonance frequency of the vehicle body means modifying the original transfer function of the vehicle body into a new transfer function of the vehicle body:

[0067]

[0068] where b is the distribution position of the actuator, g and f are the gains corresponding to the vehicle body vibration displacement response and vibration velocity response. H(s) is the vehicle body transfer function before applying control, is the vehicle body transfer function after applying control, s = jω, ω is the frequency.

[0069] Then, calculate the corresponding gains g and f according to the following formula:

[0070] (g + μ k f) T H(μ k )b = -1, k = 1, 2,..., 2n

[0071] Define r k = H(μ k )b to obtain

[0072]

[0073] The gains g and f corresponding to the vehicle body vibration displacement response and vibration velocity response can be obtained by inverting the G matrix.

[0074] Next, when the vehicle is in operation, measure and obtain the vibration displacement and vibration velocity signals at the sensor positions on the vehicle body; calculate the control force that needs to be applied to the vehicle body by multiplying the vehicle body vibration displacement and vehicle body vibration velocity by their respective corresponding gains:

[0075] Finally, by installing actuators at key parts of the vehicle body, apply the feedback control force Fc = bu(t) to the vehicle body to achieve the control of the low - frequency drumming sound inside the vehicle. Here, the piezoelectric stack actuator is selected as the actuator, which can be directly bonded to the back door of the vehicle with strong glue for testing.

[0076] The above method can modify the resonance frequencies of multiple vehicle bodies during the process of modifying the vehicle body transfer function, so as to achieve the simultaneous control of multiple resonance frequencies of the vehicle body. Specifically, by modifying multiple sets of μ k f T in the equation (g + μ k )b = -1 k values to achieve this.

[0077] In addition, the above method can also only modify specific vehicle body resonance frequencies to achieve selective control of a specific resonance frequency of the vehicle body. Specifically, by modifying a specific set of μ k f T in the equation (g + μ k )b = -1 k values to achieve this.

[0078] The following uses two actual control cases to illustrate the control effect of this method on vehicle interior noise (the dashed line is before control, and the solid line is after control).

[0079] 1. Control case 1:

[0080] Control description: As Figure 3 shown, the displacements and velocity responses at positions s1 and s2 on the elastic plate are measured by 2 vibration sensors, and a control force is applied at position s1 on the elastic plate by 1 actuator.

[0081] Control objective: Reduce the first 2-order vibration amplitudes of the plate and the corresponding sound pressure in the cavity (141 Hz, 157 H z z).

[0082] Control effect: As Figure 4 shown, the sound pressure in the cavity caused by the first-order vibration mode of the plate is reduced by 9 dB. The sound pressure in the cavity caused by the second-order vibration mode of the plate is reduced by 5 dB.

[0083] 2. Control case 2

[0084] Control description: As Figure 5 shown, the displacements and velocity responses at positions s1, s2, s3, and s4 on the elastic plate are measured by 4 vibration sensors, and control forces are applied at positions s1 and s2 on the elastic plate by 2 actuators.

[0085] Control objective: Increase the first 4-order characteristic frequencies of the elastic plate by +3 Hz, +8 Hz, +6 Hz, and +18 Hz respectively. Reduce the first 4-order vibration amplitudes of the plate and the corresponding sound pressure in the cavity (141 Hz, 157 Hz, 184 Hz, 222 Hz).

[0086] Control effect: As Figure 6As shown, the sound pressure in the cavity caused by the first four vibration modes of the plate decreases, and the corresponding frequencies shift to the right.

Claims

1. A method for controlling low-frequency road noise inside an automobile, characterized in that, Including the steps: Step 1, arrange vibration sensors at key parts of the vehicle body for static testing: randomly apply excitation to the vehicle, measure and obtain the vibration signals at the positions of the vibration sensors arranged on the vehicle body; Step 2, obtain the transfer function H(s) of the vehicle body by using the measured vibration signal spectrum, and analyze the resonance frequency of the vehicle body; Step 3, adjust the resonance frequency of the vehicle body according to the frequency avoidance principle that the difference between the resonance frequency of the vehicle body and the resonance frequency of the in-vehicle acoustic cavity is not less than 2 Hz; calculate the gains g and f corresponding to the vehicle body vibration displacement and the vehicle body vibration velocity according to the adjustment amplitude of the vehicle body resonance frequency and the transfer function of the vehicle body. That is, analyze the resonance frequency of the vehicle body by using the measured vehicle body vibration signal. When the external excitation frequency is close to this resonance frequency, the vibration amplitude of the vehicle body is amplified. Therefore, the vehicle body resonance frequency is the pole of the vehicle body transfer function. Replace the original resonance frequency of the vehicle body with a new frequency by increasing the method of active feedback control, thereby modifying the transfer function of the vehicle body, and then calculate the corresponding gains g and f; Step 4, measure and obtain the vibration displacement and vibration velocity signals at the positions of the sensors on the vehicle body when the vehicle is in operation; calculate the control force that needs to be applied to the vehicle body by multiplying the vehicle body vibration displacement and the vehicle body vibration velocity by their respective corresponding gains: where x(t) is the measured body vibration displacement, is the measured body vibration velocity; T is the transpose symbol; Step 5, install actuators at key parts of the vehicle body, and apply a feedback control force Fc = bu(t) to the vehicle body to achieve the purpose of modifying the transfer function of the vehicle body and further controlling the low-frequency road noise in the vehicle, where b is the position vector of the feedback force.

2. The method for controlling low-frequency road noise inside an automobile according to claim 1, wherein The said step 2 is based on the spectrum J(ω) of the measured vehicle body vibration signal, where ω is the frequency, and performs Laplace transform s = jω on it. The transfer function of the vehicle body is obtained as J(s).

3. The method for controlling low-frequency road noise inside an automobile according to claim 1, wherein Modifying the transfer function of the vehicle body means modifying the original transfer function H(s) of the vehicle body into a new transfer function of the vehicle body: b is the distribution position of the actuator, g and f are the gains corresponding to the vibration displacement response and the vibration velocity response of the body measurement point position, H(s) is the body transfer function before applying control, is the body transfer function after applying control, s = jω, ω is the frequency.

4. The method for controlling low-frequency road noise inside an automobile according to claim 3, characterized in that, Calculate the system gains g and f according to the following formula: (g + μ k f) T H(μ k )b = -1, k = 1, 2, ···, 2n Define r k = H(μ k )b is obtained By inverting the G matrix, the gains g, f, and μ corresponding to the vibration displacement response and vibration velocity response at the positions of the sensors on the vehicle body can be obtained. k is the resonance frequency of the vehicle body after applying the control.

5. The method for controlling low-frequency road noise inside an automobile according to claim 4, characterized in that During the process of modifying the vehicle body transfer function, the resonance frequencies of multiple vehicle bodies can be modified, that is, by modifying multiple sets of μ values in the equation (g + μ k f) T H(μ k )b = -1 to achieve the simultaneous control of multiple resonance frequencies of the vehicle body. k ​ 6. The method for controlling low-frequency road noise inside an automobile according to claim 4, characterized in that, During the process of modifying the vehicle body transfer function, the resonance frequencies of multiple vehicle bodies can be modified, that is, by modifying multiple sets of μ k f T in the equation (g + μ k )b = -1, so as to control multiple resonance frequencies of the vehicle body simultaneously. k The values are obtained to control multiple resonance frequencies of the vehicle body simultaneously.

7. The method for controlling low-frequency road noise inside an automobile according to claim 4, wherein During the process of modifying the vehicle body transfer function, only specific vehicle body resonance frequencies are modified, that is, by modifying a specific group of μ k f T in the equation (g + μ k )b = -1, the value of μ k is modified to achieve selective control of a specific resonance frequency of the vehicle body.

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