With the intensification of environmental protection policies and energy shortages, the domestic electric vehicle market has gradually risen. The Chinese electric vehicle market has gradually attracted worldwide attention, and the domestic market has also become the main global electric vehicle market. With the increasing number of electric vehicle users and the continuous improvement of electric technology, various performance requirements for electric vehicles will continue to increase. As a basic problem in electric vehicles, noise issues cannot be ignored in the development process of electric vehicles. In terms of braking assistance for electric vehicles, the current combination of electric vacuum pumps and electric boosters is mainly used. Electric vehicles have got rid of their dependence on traditional fuel engines. Therefore, traditional intake manifold technology cannot be used on engines. A separate vacuum pump system provides vacuum; when the electric vacuum pump works, it is affected by structure and speed, and noise often occurs. Especially after excluding engine noise, the noise of the vacuum pump will be more prominent. Therefore, how to reduce the noise of vacuum pumps has become the main concern and problem of car companies.
、电动汽车真空泵应用现状 1. Application status of electric vehicle vacuum pump
The vacuum pumps of current electric vehicles can be divided into three types: piston electric vacuum pumps, diaphragm electric vacuum pumps and vane electric vacuum pumps. These types of vacuum pumps have certain differences in form and structure. Each has its advantages and disadvantages, so it is different in different models. Has unused applications. Affected by development and historical reasons, the current situation is mainly the vane electric vacuum pump. During the high-speed operation of the vane vacuum pump, the metal inner wall structure will rub against the graphite blade, causing impact or noise.
In combination with the overall situation of electric vehicles, the main indicators of electric vacuum pumps are cost, weight, durability, size, vibration and noise. Due to the impact of durability, piston-type electric vacuum pumps are mostly used in vulgar electric vehicles. At the same time, they have limited reliability requirements and low braking performance. Therefore, the models are mainly low-end. 。 The main disadvantages of the diaphragm type electric vacuum pump are the large size of the working cavity and the diaphragm, the structure of the double diaphragm appears horizontally, and the push rod performs cyclic reciprocation in the cavity, so the vibration during work is strong. Moreover, the cost of parts is relatively high, but compared with the vane electric vacuum pump, the noise control ability is better, and the noise is relatively low by 8-9dB . This type of vacuum pump is used in vehicles with lower requirements on the layout of the entire vehicle. The cost requirement is used in vehicles with low cost requirements and better noise control capabilities.
Noise analysis of vane electric vacuum pump. 左右，因此存在高频震动现象，虽然电动真空泵配备了橡胶垫进行减震，但是安装位置上如果不进行合理设置，安装于车架上时就会造成高频震动到传递到驾驶室内，影响驾驶体验。 The speed of the vane-type electric vacuum pump is about 5000r / s , so there is a high-frequency vibration phenomenon. Although the electric vacuum pump is equipped with a rubber pad to reduce vibration, if the installation position is not properly set, it will be installed on the frame. Will cause high-frequency vibration to be transmitted to the cab, affecting the driving experience. In order to reduce the vibration transmission performance of the pump body and make it fully attenuated, the electric vacuum pump can be placed on the reducer or motor of the front-wheel drive vehicle, and its vibration can be attenuated twice by the suspension device, so it can effectively reduce The noise of the electric vacuum pump is conducted through the entire vehicle; since the noise can be transmitted through the air, the design of the electric vacuum pump can be set on the diagonal line furthest from the cab to reduce the transmission of noise. After the position of the vane vacuum pump is selected, the structural design and simulation analysis of the connection bracket are needed to understand the resonance phenomenon that may exist in the mechanical structure and reduce the noise generated by the resonance.
The diaphragm electric vacuum pump is composed of a pump body and a motor. It is characterized in that the inlet and exhaust ports are on the pump body. Both ends of the port contain symmetrical piston components, including piston rods, metal inserts and diaphragms. The ring is directly connected to the pump body. One end of the bearing sub-loading piston rod is connected with the eccentric mandrel to the bearing. The motor output shaft and the mandrel are turned into an interference fit. The mandrel is driven by the motor to rotate and simultaneously drive the piston assembly to Movement; the diaphragm deforms under the action of the piston connecting rod. When it is at a dead point, the space in the diaphragm is the largest. When it is in the suction state, a negative pressure is formed in the diaphragm, and suction is generated, otherwise it is in an exhaust state. In order to ensure that the vacuum pump is in a balanced state, a weight is often provided on the pump body.
The piston vacuum pump is also called a reciprocating vacuum pump. It mainly depends on the reciprocating movement of the piston in the cylinder to realize the suction and discharge of gas. Piston vacuum pumps are divided into vertical and horizontal, and there are also single and double cylinders, so the exhaust valve is also divided into free valve and slide valve. The piston vacuum pump is not affected by water vapor, has a stable structure and is easy to operate, but the ultimate vacuum is not high.
、电动汽车真空泵噪音问题的分析 2. Analysis of the noise problem of electric vehicle vacuum pump
Take a low-speed electric vehicle as an example for analysis. The electric vacuum pump is of the piston type. The DC motor is directly connected to the installed eccentric wheel. Under the operation of the motor, the left and right symmetrical pistons are driven by the eccentric wheel to make the piston reciprocate. The flexible piston fitting on the piston can seal the structure well and reduce the Friction between the cylinder and the piston. Based on the movement of the piston, the volume between the piston and the intake valve is periodically expanded and contracted to ensure that the air pressure in the cylinder is periodically changed to achieve a single transmission of airflow and provide a vacuum environment for the system.
Combining the feedback from the development process with the use of the car, it can be found that the vibration noise between the electric car and the vacuum pump is mainly affected by the following issues:
① The connection between the electric vacuum pump and the vehicle is unreasonably set, which causes the shock absorption effect to decrease, and the vibration is directly transmitted to the cab or the vehicle structure.
② There is a certain vibration frequency of the vacuum pump system formed by the electric vacuum pump and the bracket. If the natural frequencies of the components on the electric vehicle are not fully considered, the two may be similar, causing the resonance of the vacuum pump system.
③ The position design of the electric vacuum pump is unreasonable. The vacuum pump is located in a thin wing plate and other parts of the automobile structure, resulting in intensified vibration and enhanced vibration transmission.
④ The electric vacuum pump is affected by its structure, which causes an increase in vibration and noise.
⑤ The pumping efficiency setting of the electric vacuum pump is unreasonable. The brake link of electric vehicles has higher requirements for vacuum, so it is necessary to set a vacuum pump or increase the vacuum pump efficiency. When the suction efficiency of the electric vacuum pump is greatly reduced in the second half, an excessively low degree of vacuum may cause an abnormal pressure difference between the two sides of the air valve, causing abnormal noise of the vacuum booster.
⑥ The pneumatic threshold setting of the electric vacuum pump is unreasonable. The vacuum pump start-stop threshold greatly affects the working time of the vacuum pump. Once the starting threshold of the vacuum pump exceeds the standard value, the number of starts of the vacuum pump will be greatly increased; once the starting threshold of the vacuum pump is too low, the single start time of the electric vacuum pump will be increased, resulting in the extension of the working time of the vacuum pump , So we need to adjust the start-up time and start-up times in accordance with actual needs to find a reasonable match.
、电动汽车真空泵噪音问题的对策 3 , countermeasures against noise problems of vacuum pumps for electric vehicles
For this kind of problem, the following directions need to be adjusted to reduce the impact of vibration and noise:
① Improve the secondary shock absorption effect. The vacuum pump of electric vehicles is often connected to the bracket through the primary shock absorption unit, and then the entire bracket is fixed by the bolt and nut structure to achieve the connection with the vehicle body. At this time, rubber pads can be added at the connection site. Reduce the vibration effect at the connection, and form secondary vibration isolation.
② In the traditional design, in order to improve the shock absorption, more shock pads are often used, which greatly increases the vibration transmission effect. At this time, the number of shock pads can be appropriately reduced to reduce the vibration transmission effect.
③ Adjust the layout of electric vacuum pumps on electric vehicles, and set the vacuum pumps at locations with high rigidity and strength to avoid direct connection with thin-walled structures; electric vacuum pumps can be connected to large-scale systems such as gearboxes and motors , Make full use of the original independent damping mechanism to reduce the transmission effect of vibration.
④ Adjust the form of the vacuum tube so that it is consistent with the gas distribution requirements of electric vehicles; the position and number of buckles on the vacuum tube can also be adjusted to reduce the occurrence of vibration.
⑤ Properly increase the suction efficiency of the electric vacuum pump. If the extraction efficiency is set unreasonably and the value is relatively low, the single working time of the electric vacuum pump will increase. Therefore, this value can be appropriately raised to reduce the continuous working time of the vacuum pump.
⑥ Reasonably adjust the starting threshold of the vacuum pump. The vehicle speed sensor system is adopted, and the vehicle speed is used as the basis for data adjustment to determine road conditions. If the vehicle speed is not high, the surrounding environment is mostly congested. Therefore, the starting frequency can be greatly reduced by reducing the starting threshold value. At this time, reducing the starting threshold value will not reduce the braking force provided to the car, because the vehicle speed is limited and can meet the design. Requirements; if the driving speed is high, a lower braking frequency is required, and the braking force is required to be larger, at this time the vacuum pump start threshold should be appropriately raised.
⑦ Replace the form of electric vacuum pump. By adding weights to the bracket of the electric vacuum pump, the stability of the bracket can be increased, and the transmission of vibration can be reduced. Experiments have proved that the noise can be effectively controlled when the weight is not increased. You can also choose a low-noise diaphragm vacuum pump. The change of the vacuum pump can reduce the control of noise to a minimum level, especially high-frequency noise and vibration can be effectively controlled.
According to the specific application environment of the electric vacuum pump, to reduce the noise of the vacuum pump, you can use the following measures to adjust:
① Improve the sealing performance of the front cabin of the car. By improving the airtightness of the cabin, the transmission of noise to the outside can be reduced, the purpose of controlling noise inside, and reducing the diffusion of noise to the outside can be achieved.
② Regarding the exhaust noise of the electric vacuum pump, although the noise is relatively small as a whole, it is easy to control. By installing hoses and other measures, the noise can be controlled to a lower range to reduce noise.
③ Adjusting the power of the electric vacuum pump, under the premise of satisfying the extraction efficiency, appropriately reducing the power can achieve a certain noise reduction purpose.
④ Improve the structure of the vacuum tank, adopt a new design, optimize the body of the vacuum tank, reduce the vibration of the tank, especially the connection position between the body and the tank, and adopt vibration isolation treatment to improve the vibration isolation effect and reduce the vacuum tank to the car body The transmitted vibration improves the vibration noise in the car.
Electric vehicles have got rid of their reliance on traditional fuel engines and mainly use batteries for power supply, so noise outside the engine will be very obvious. The noise control of the whole vehicle has become the focus of the car design. Therefore, the noise of the vacuum pump should be paid attention to in the subsequent design of the electric vehicle. Based on the current application status of electric vehicle vacuum pumps, this paper points out the common vacuum pump classification and the potential influencing factors of noise, and provides guidance for subsequent noise analysis. Then, it analyzes the influencing factors of electric vehicle vacuum pump noise and finally proposes targeted noise improvement countermeasures. The level of control of electric vehicle noise has been greatly improved.
For more feasibility analysis of electric vehicle vacuum pump system, please download attachment: Feasibility analysis of vacuum pump system