A method of avoiding engine and fan beat frequencies

Abstract

The present application relates to a kind of methods for avoiding engine and fan beat frequency, according to the noise vibration data in vehicle, obtain beat frequency speed interval, the beat frequency speed interval is the speed interval of fan when engine and fan produce beat frequency when test vehicle is in idle speed condition and engine speed is preset speed;Determine whether the speed of fan is not located in the beat frequency speed interval meets the heat dissipation demand;If not, the main contribution factor of noise is obtained by the noise vibration data in vehicle, and then the main contribution factor is based on the main contribution factor optimization vehicle body structure, the main contribution factor is the excitation produced when fan rotates or the excitation produced when engine rotates.The present application can effectively reduce the influence of beat frequency, and has good inhibitory effect on beat frequency.

Description

Technical Field

[0001] This invention relates to the field of automotive engineering technology, specifically to control technology for idling speed beat frequency problems. Background Technology

[0002] Currently, with the rapid development of automotive technology, the technical standards for both traditional and new energy hybrid vehicles are becoming increasingly stringent, leading to higher demands for vehicle thermal management. This, in turn, places higher and more precise requirements on the heat dissipation capabilities of automotive cooling fans. Consequently, high-airflow, high-speed cooling fans are being used more and more extensively.

[0003] This leads to a series of NVH performance issues with cooling fans, with idle beat frequency being the most significant. Beat frequency is a rhythmic, periodic change in sound or vibration over time, which can easily cause discomfort. The main reason is the presence of two excitation signals with similar frequencies and amplitudes; their combined signal exhibits periodic amplitude variations, resulting in subjectively fluctuating sound or vibration, which is highly likely to cause discomfort and therefore requires close attention and control.

[0004] The noise and vibration generated by automotive cooling fans mainly include: first-order vibration noise caused by fan imbalance; BPF pulsation noise corresponding to the number of blades generated when the fan blades cut through the air; and eddy noise generated by the compression and rarefaction processes of the surrounding gas caused by the fan rotation. Since automotive cooling fans generally operate at speeds below 3000 rpm, their first-order frequency (1st-order frequency = fan speed / 60) is generally below 50Hz. This is close to the second-order frequency of most car engines at idle speed (generally between 700-1400 rpm) (2nd-order frequency = engine speed / 30, ignition excitation for 4-cylinder engines), thus easily leading to frequency beat issues. Summary of the Invention

[0005] The purpose of this invention is to provide a method to avoid engine and fan frequency mismatch, thereby solving the problem of fan and engine frequency mismatch.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method to avoid engine and fan beat frequency.

[0008] Based on the in-vehicle noise and vibration data, the beat frequency speed range is obtained. The beat frequency speed range is the speed range of the fan when the engine and fan generate beat frequency when the test vehicle is idling and the engine speed is at a preset speed.

[0009] Determine whether the heat dissipation requirement is met when the fan speed is not within the beat frequency speed range;

[0010] If the conditions are not met, the main contributing factors of the noise are obtained through in-vehicle noise and vibration data, and then the vehicle body structure is optimized based on the main contributing factors, which are the excitation generated when the fan rotates or the excitation generated when the engine rotates.

[0011] Based on the above technical means, the first step is to determine whether changing the fan speed can avoid the frequency spike by judging whether the fan speed can meet the heat dissipation requirements by avoiding the frequency spike range. If it does not meet the requirements, the vehicle body structure is optimized based on the main contributing factors, which can effectively solve the problem of fan and engine frequency spike. Furthermore, the frequency spike range and heat dissipation requirements are both objective values. Therefore, the technical means of suppressing frequency spike based on objective values ​​has a better suppression effect.

[0012] Furthermore, when the excitation generated when the fan rotates is the main contributing factor, the dynamic stiffness of the fan's cooling module vibration isolation pad is reduced by 10-100Hz, while the dynamic stiffness of the vehicle body side cooling module mounting point is increased by 10-100Hz.

[0013] Furthermore, when the excitation generated when the engine rotates is the main contributing factor, the structure that resonates with the excitation generated when the vehicle body rotates and the engine rotates is identified, and then that structure is strengthened.

[0014] Furthermore, the method for obtaining the beat frequency speed range is as follows: start the test vehicle, set the test vehicle to idle speed, and set the engine speed of the test vehicle to a preset speed;

[0015] Start the fan and gradually increase its speed from the lowest setting to generate a time-domain response curve;

[0016] The beat frequency speed range is obtained based on the time-domain response curve.

[0017] Furthermore, the fan speed increases at a constant rate. A beat frequency band is extracted from the time-domain response curve. The difference between the peak and trough of the beat frequency band is greater than a preset difference. The time history corresponding to the beat frequency band is then converted into the fan speed range.

[0018] Furthermore, the main contributing factors are the first-order excitation generated when the fan rotates or the second-order excitation generated when the engine is working.

[0019] Furthermore, the second-order frequency of the engine corresponding to the preset speed is lower or higher than the first-order frequency corresponding to the maximum fan speed, with a difference of not less than 5Hz.

[0020] Furthermore, the preset difference value is 3dB.

[0021] The beneficial effects of this invention are:

[0022] This invention pre-plans the fan speed, pre-designs the fan speed and idle speed to avoid frequency spikes, and then determines whether the fan speed can be controlled to avoid frequency spikes by checking whether the heat dissipation requirements are met. If the requirements are not met, the vehicle body structure is optimized based on the main contributing factors of vehicle body noise data. This method can effectively reduce the impact of frequency spikes and has a good suppression effect on frequency spikes. Attached Figure Description

[0023] Figure 1 Flowchart of this embodiment;

[0024] Figure 2 Combined signal of fan excitation and engine excitation: time-amplitude relationship graph;

[0025] Figure 3 Time-amplitude (dBA): A graph showing the relationship between the effective value of the frequency band between f1 and f2 and time.

[0026] Figure 4 Frequency-in-vehicle noise amplitude (Pa): Noise spectrum diagram of the driver's right ear when the beat frequency occurs. Detailed Implementation

[0027] The following description, with reference to the accompanying drawings and preferred embodiments, illustrates the implementation of the technical solution of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention and not for limiting the scope of protection of the present invention.

[0028] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0029] This embodiment proposes a method to avoid engine and fan frequency beat-offs. The method is summarized as follows: In a semi-anechoic chamber, the engine is controlled at the required idle speed. A microphone is placed at the driver's right ear inside the vehicle, and a vibration sensor is placed at the 12 o'clock position on the steering wheel. The noise and vibration data of the fan are tested from low to high speeds (the fan acceleration rate should be less than or equal to 10 rpm / s, which can be adjusted according to specific conditions). Through data analysis and subjective evaluation, the speed range of the fan beat-off frequency is determined. This can be divided into two cases: 1. If the fan does not operate within the beat-off frequency range while meeting the cooling requirements, then an acceptable fan speed is selected as the cooling setting, and the beat-off frequency problem is solved; 2. If the fan must operate within the beat-off frequency range due to cooling or other reasons, then the main contributor can be determined by separately testing the in-vehicle noise and vibration data of the cooling fan and the engine operating independently, thus clarifying the direction for rectification.

[0030] On the vehicle, the fan is controlled via external devices to operate from low to high speeds. Simultaneously, noise and vibration sensors are deployed inside the vehicle to obtain fan noise and vibration data corresponding to the points of frequency fluctuation issues. This data can be used to identify the speed range of fan and engine frequency fluctuations and their main contributors, thus defining the direction for rectification (primarily two directions: reducing the first-order excitation of the fan and reducing the second-order excitation of the engine). The specific theoretical formulas are as follows:

[0031] Fan noise signal: A1 fan first-order excitation amplitude, First-order fan frequency;

[0032] Start noise signal: A2 engine second-order excitation amplitude, Engine second-order frequency;

[0033] Combined signal of fan and engine noise: The synthesized signal, i.e., the beat frequency signal, can be converted into: in The amplitude of the synthesized signal is ; the frequency of the beat frequency signal is . Its signal waveform is as follows Figure 2 As shown, the value of the peak is (A1+A2); the value of the trough is |A1-A2|; the difference between the peak and trough of the synthesized signal is B=(A1+A2)-(|A1-A2|).

[0034] According to the definition of beat frequency, beat frequency is the phenomenon where noise or vibration fluctuates after two signals with similar frequencies are combined. Therefore, it is necessary to control the difference between the peaks and troughs of the combined signal, i.e., B must be sufficiently small. Reducing one or both of A1 and A2 can reduce the value of B, thus effectively solving the beat frequency problem. In actual testing, the peak-to-peak value is usually read by extracting the effective value curve of the frequency band between f1 and f2 over time, i.e., the difference between the peaks and troughs (the noise difference is generally expressed in dBA: ≤3dBA is required).

[0035] Specifically, the method proposed in this embodiment includes the following steps:

[0036] S10: In the vehicle state, in the semi-anechoic chamber, the cooling fan is driven and controlled by external power supply and control equipment on the vehicle to enable it to accelerate and maintain a stable speed; and a microphone is placed at the driver's right ear inside the vehicle, and a vibration sensor can be placed at the 12 o'clock position of the steering wheel when needed.

[0037] S20: Unplug the vehicle cooling fan connector and replace it with an external power supply and control so that the fan operating speed can be changed.

[0038] S30: Start the vehicle and bring the engine to normal idle speed. At this time, control the fan to run at low speed (in increments of 50 rpm) and test the vibration and noise data of the fan at a stable speed (e.g., 1000 rpm, 1050 rpm, etc.). Warm up the vehicle for 10 minutes. The engine idle speed should correspond to an engine second-order frequency that is 5 Hz lower or higher than the first-order frequency of the fan's maximum operating speed.

[0039] S40: Control the fan speed from the lowest speed in 50 rpm increments up to the highest speed, test the noise and vibration at each fan speed, and generate a time-domain curve of the vibration. The type of the time-domain curve is as follows: Figure 3 As shown, this is used to identify the beat frequency rotation speed point. In S40, due to the setting of the gradient, the fan speed at a certain moment can be calculated based on time.

[0040] S50: Analyze the test data to determine the beat frequency and rotation speed range.

[0041] In S50, the beat frequency band between f1 and f2 is first extracted from the time-domain curve. The difference between the peak and the trough in the beat frequency band is greater than the preset difference. In this embodiment, the preset difference is 3dBA. Then, the fan speed is deduced by using the horizontal axis time to obtain the beat frequency speed range. The beat frequency speed range is defined as the fan speed range when the engine and fan generate beat frequency when the test vehicle is idling and the engine speed is at the preset speed.

[0042] S60: Prevents the fan from operating within the beat frequency speed range and determines whether the vehicle's cooling requirements are met. For example, if the fan speed is 1700-2000 rpm and the engine beat frequency (1050 rpm idle), and the vehicle's cooling requirements require the fan to operate at speeds greater than 1700 rpm, then the speed signal input to the fan can be adjusted to 2000 rpm or higher through the vehicle's thermal management calibration software to avoid the fan beat frequency speed range.

[0043] Furthermore, if the fan speed beat (e.g., the fan speed of 1700-2000 rpm clashes with the engine beat (idle speed 1050 rpm), and the vehicle's cooling requirements necessitate the fan operating at speeds greater than 1700 rpm, then the input speed signal to the fan can be adjusted to 2000 rpm or higher via the vehicle's thermal management calibration software to avoid the fan beat range) while simultaneously meeting cooling requirements, the beat issue is resolved. If it is not met, further optimization is required, proceeding to S70.

[0044] S70: If the heat dissipation requirements are not met, it is necessary to analyze the test data of fan beat frequency and speed to determine the main contributors to the fan and engine excitation. This can be determined by analyzing previously tested in-vehicle noise and vibration data at different fan speeds during idle (first-order fan excitation, second-order engine excitation). If A1 > A2, the fan is the main contributor; otherwise, it is the engine. Figure 4 The image shows the engine's second-order excitation as the primary excitation. In actual testing, based on the noise spectrum of the driver's right ear at the beat frequency obtained from the actual test: it is generally required that the first-order noise of the fan be less than 30 dB(A), and the first-order vibration amplitude of the steering wheel fan in one direction be less than 20 mg. If the first-order noise and vibration of the fan are too large, they are optimized; otherwise, the second-order noise and vibration of the engine are optimized.

[0045] Therefore, if the first-order noise of the fan is the main contributor, proceed to S80; if the second-order excitation of the engine is the main contributor, proceed to S90.

[0046] Step 80: If the issue is first-order noise and vibration from the fan, the dynamic stiffness of the cooling module's mounting point on the vehicle body side, the static imbalance of the electric fan, and the dynamic stiffness of the cooling module's rubber pads need to be controlled (these indicators should be standardized based on engineering experience, controlled during the early design phase, and adjusted later based on actual vehicle performance). For example, increasing the dynamic stiffness of the cooling module's mounting point on the vehicle body side (5-100Hz), reducing the static imbalance of the cooling fan, and reducing the stiffness of the cooling module's vibration damping pads (5-100Hz) can all increase the vibration isolation of the cooling fan module's vibration damping pads, effectively reducing the first-order vibration of the cooling fan.

[0047] Step 90: If the engine's second-order noise is the primary excitation, it is necessary to identify local body modes and improve the vibration isolation of the corresponding frequency bands, such as reducing the sensitivity of the body transmission paths such as the sunroof, roof, and tailgate. Identify the resonance locations of the corresponding second-order frequencies inside the vehicle, such as the sunroof front crossbeam and tailgate modes, and formulate reinforcement plans at the corresponding locations; or reselect the engine idle speed to avoid the frequency of the in-vehicle modes, in order to reduce the engine's second-order noise inside the vehicle; or take active noise reduction measures to reduce the engine's second-order noise.

[0048] Step 100: Determine if the beat frequency problem has been resolved. If not, return to S70; if resolved, end the process.

[0049] The characteristics of this method are: 1. In the early design stage, the idle speed and the maximum speed of the cooling fan are planned in advance to avoid frequency fluctuations (to meet heat dissipation performance while retaining the maximum fan speed); 2. Due to different heat dissipation requirements, the operating speed of the cooling fan is controlled by the overall vehicle heat load, but during the software calibration process, the operating speed range can be purposefully selected to avoid frequency fluctuations; 3. If frequency fluctuations cannot be avoided due to heat dissipation or other reasons, the first-order excitation of the fan or the second-order excitation of the engine can be optimized by combining test data.

[0050] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A method for avoiding engine and fan frequency fluctuations, characterized in that: Based on the in-vehicle noise and vibration data, the beat frequency speed range is obtained. The beat frequency speed range is the speed range of the fan when the engine and fan generate beat frequency when the test vehicle is idling and the engine speed is at a preset speed. Determine whether the heat dissipation requirement is met when the fan speed is not within the beat frequency speed range; If not, the main contributing factors of the noise are obtained through in-vehicle noise and vibration data, and then the vehicle body structure is optimized based on the main contributing factors, which are the excitation generated when the fan rotates or the excitation generated when the engine rotates. When the excitation generated when the fan rotates is the main contributing factor, the dynamic stiffness of the fan's cooling module vibration isolation pad is reduced by 10~100Hz, while the dynamic stiffness of the cooling module mounting point on the vehicle body side is increased by 10~100Hz. The second-order frequency of the engine corresponding to the preset speed is lower or higher than the first-order frequency corresponding to the maximum fan speed, with a difference of not less than 5Hz.

2. The method for avoiding engine and fan frequency fluctuations according to claim 1, characterized in that: When the excitation generated when the engine rotates is the main contributing factor, identify the structure in which the vehicle body resonates with the excitation generated when the engine rotates, and then strengthen that structure.

3. The method for avoiding engine and fan frequency fluctuations according to claim 1, characterized in that: The method for obtaining the beat frequency speed range is as follows: start the test vehicle, set the test vehicle to idle speed, and set the engine speed of the test vehicle to the preset speed; Start the fan and gradually increase its speed from the lowest setting to generate a time-domain response curve; The beat frequency speed range is obtained based on the time-domain response curve.

4. The method for avoiding engine and fan frequency fluctuations according to claim 3, characterized in that: The fan speed increases at a constant rate. A beat frequency band is extracted from the time-domain response curve. The difference between the peak and trough of the beat frequency band is greater than a preset difference. The time history corresponding to the beat frequency band is then converted into the fan speed range.

5. The method for avoiding engine and fan frequency fluctuations according to claim 1, characterized in that: The main contributing factors are the first-order excitation generated when the fan rotates or the second-order excitation generated when the engine is working.

6. The method for avoiding engine and fan frequency fluctuations according to claim 4, characterized in that: The preset difference is 3dB.

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