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Solution to the problem of insufficient vacuum pumping capacity
Source of information: Datong official website Date: 2020-01-15

吨的柴油发动机车辆。 The application of the vacuum pump system in automobiles originated from the requirements of braking systems, especially diesel-engine vehicles with a total vehicle weight of less than 5 tons. Due to the overall arrangement and engine limitations, other boosters such as compressors cannot be reasonably configured, which results in the disadvantages of large braking power and low comfort. Therefore, other assistance systems are needed to make up for this shortcoming.

The vacuum pump is small in size, high in reliability, and convenient in layout, and almost no changes are made to the entire vehicle, so the vacuum pump is applied in the entire vehicle. With the development of automotive technology, as a power source, vacuum pumps are increasingly used in automobiles. Vacuum pumps are the vacuum source of vacuum pump systems . When the vacuum of the engine intake pipe is insufficient or not, it is a certain part of the automobile. Provide vacuum, such as vacuum brake booster. If the vacuum pump is not capable of evacuating, it will make continuous braking effort, product flow to the market will affect the brand image and reduce customer satisfaction.

In this paper, the vacuum pumping capacity of a diesel engine vacuum pump is insufficient, and the vacuum pump structure is optimized to improve the performance of the vacuum pump.

真空泵简介 1 Vacuum Pump Introduction

现状描述 1.1 Status description

During the development phase of a complete vehicle project, it was found that there was a problem of continuous braking effort. After investigation, the cause of continuous braking effort was the insufficient performance of the vacuum pump.

单叶片式真空泵简介 1.2 Introduction of Single Vane Vacuum Pump

The vacuum pump described in this article is a single vane vacuum pump. The driving torque rotates the rotor through the engine camshaft and the vacuum pump connector, thereby driving the single vane along the contour of the vacuum pump cavity and rotating at the eccentric position of the cavity. The upper and lower sides of a single blade are divided into two chambers, and the upper side is a vacuum chamber. As the volume of the single blade rotates, the volume of the chamber becomes larger and larger, thereby generating a degree of vacuum. At the same time, it is connected to a vacuum booster with a unidirectional The air inlet of the valve increases the vacuum of the vacuum booster. The lower cavity is a compression cavity. With the rotation of the single blade, the volume of the cavity is getting smaller and smaller, compressing the lubricating oil and the air extracted from the vacuum booster to the engine. .

性能测试方法及目前性能 1.3 Performance test methods and current performance

After the engine warms up for a while, the engine will stop. Press the brake to consume the vacuum in the vacuum booster until the vacuum reading is zero. After starting the engine (idle speed, air-conditioning compressor does not turn on), start to measure the vacuum in the vacuum pump tube. 至80kPa ,每隔10kPa记录时间,共测试两组数据,取平均值。 From 0kPa to 80kPa , record time every 10kPa , test two sets of data and take the average.

优化分析 2 optimization analysis

After disassembly of the vacuum pump, it was found that, because the pump cavity is much larger than the rotor diameter, the sealing surface formed here is extremely small, almost a line seal, and the sealing effect cannot be guaranteed well. As a result, the degree of vacuum in the vacuum chamber is increased slowly. At the same time, the sealing gap between the pump cavity and the rotor is greatly affected by the size and position of the screw hole. The gap here may be enlarged during assembly, which further reduces the sealing effect.

Through the above analysis, it is determined that the main reason for the insufficient performance of the vacuum pump is that the internal intake and exhaust chambers of the pump cavity are not well sealed and cross each other. The specific problems are summarized as follows:

泵腔型线为圆滑椭圆,与转子间隙油密封为线密封,泵腔内部压力太大,线密封密封效果不理想,真空泵运行时吸气腔室和排气腔室相贯通,抽气效率降低; The shape of the pump cavity is round and oval, and the oil seal with the rotor gap is a line seal. The internal pressure of the pump cavity is too large, and the line seal is not ideal. The suction chamber and the exhaust chamber are connected when the vacuum pump is running. reduce;

泵盖位置度过大导致泵腔壁与转子间隙变化太大,引起泵腔壁与转子间隙处密封不良。 B The position of the pump cover is too large, which causes the gap between the pump cavity wall and the rotor to change too much, resulting in a poor seal at the gap between the pump cavity wall and the rotor. It can be seen by zooming in the low-temperature exothermic curve that the larger the injection advance angle, the earlier the exothermic rate curve. However, when the fuel injection advance angle is further advanced, the heat release will be delayed, because when the fuel injection advance angle is large, the mixture in the cylinder is more uniform, so that the diesel is thinly distributed in the cylinder, reducing the area with high activity.

整改措施 3 Rectification measures

Adding a small circular arc with the rotor in the pump cavity changes the local profile of the pump cavity and moves the eccentricity of the rotor at the same time, so that the rotor can fit the sealing surface of the pump cavity well and enhance the sealing effect. In order to ensure that the matching clearance between the pump cavity and the rotor does not change due to assembly, positioning pins are added at the corresponding positions of the pump body and the pump cover. The specific improvement plans are summarized as follows:

针对“泵腔型线为圆滑椭圆,与转子间隙油密封为线密封,泵腔内部压力太大,线密封密封效果不理想,真空泵运行时吸气腔室和排气腔室相贯通,抽气效率降低”问题点改进方案:更改泵腔局部线型,使转子与泵腔壁的线密封优化为面密封形式,增强密封能力,减轻泵腔进、排气腔室串气情况。 A. For the "pump cavity line is a smooth ellipse, the oil seal with the rotor gap is a line seal, the internal pressure of the pump cavity is too large, the line seal sealing effect is not ideal, the suction chamber and the exhaust chamber are connected when the vacuum pump is running. Improved solution to the problem of “lower gas efficiency”: change the local line shape of the pump cavity, optimize the line seal between the rotor and the wall of the pump cavity to form a face seal, enhance the sealing ability, and reduce the air flow between the pump cavity and the exhaust cavity.

针对“泵盖位置度过大导致泵腔壁与转子间隙变化太大,引起泵腔壁与转子间隙处密封不良”问题点改进方案: B. To improve the problem of "the pump cover position is too large, the gap between the pump cavity wall and the rotor changes too much, causing a poor seal between the pump cavity wall and the rotor gap" problem improvement plan:

Add positioning pins at the appropriate positions of the pump cover and pump body for precise positioning, thereby improving the fitting accuracy.

In summary, in order to optimize the performance of the vacuum pump, the following measures are taken:

)改变泵腔内部进排气腔室密封结构,消除相互窜气的情况,从而减少压力建立时间; 1 ) Change the seal structure of the inlet and exhaust chambers inside the pump cavity to eliminate the mutual blow-by, thereby reducing the pressure build-up time;

)在泵盖和泵体适宜位置增加定位销进行精定位,提高配合精度,减少压力损失,缩短压力建立时间。 2 ) Add positioning pins at the appropriate positions of the pump cover and pump body for precise positioning, improve the accuracy of the fit, reduce the pressure loss, and shorten the pressure build-up time.

方案验证 4 scheme verification

整改件测试 4.1 Rectification test

After the rectification plan was determined, the rectified parts were tested and verified on the entire vehicle. The vacuum pumping performance of the rectified vacuum pump was good. 的真空度时所用的时间在5s左右,达到80Kpa的真空度所需时间均不超过10s 。 When the two pieces reach a vacuum degree of 66.7Kpa , it takes about 5s , and the time required to reach a vacuum degree of 80Kpa does not exceed 10s .

整车试验 4.1 Vehicle test

小时耐久试验后,对其性能在整车上进行测试,进一步确定其提升效果。 After the rectified parts have undergone a 400- hour endurance test, their performance is tested on the entire vehicle to further determine its lifting effect. 的真空度时所用的平均时间缩短到7.53s ,达到80Kpa的真空度所需的平均时间为11.535s ,改进效果明显。 When the vacuum degree of 66.7Kpa is reached, the average time used is shortened to 7.53s , and the average time required to reach a vacuum degree of 80Kpa is 11.535s . The improvement effect is obvious.

结语 5 conclusion

Through dismantling and analysis, this paper finds out that the cause of the insufficient performance of the vacuum pump is the poor sealing of the inlet and exhaust chambers of the vacuum pump, and mutual cross-flow, which affects the vacuum pumping ability and leads to insufficient vacuum pump performance. And through the optimization of the corresponding structure, the performance of the vacuum pump is improved, and the continuous braking performance of the entire vehicle is improved.

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