来自MBA智囊百科全书（）
（从机械损失中重定向）
机械损失
目录
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什么是机械损失
机械损耗是指轴和轴密封，轴和轴承以及叶轮旋转时叶轮盘摩擦时损失的功率。
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机械损失的组成
（i）摩擦损失
（1）活塞，活塞环和气缸壁之间的摩擦损失。损失的这一部分是由于较大的滑动面积，高速度和润滑不足而导致的摩擦损失的主要部分。摩擦损失与结构因子有关，例如活塞长度，活塞间隙，活塞环数量和环张力。另外，在相同的配置下，它还随圆柱压力，活塞速度和润滑油粘度的增加而增加。
（2）轴承和阀机制之间的摩擦损失。包括所有主要轴承中的摩擦损失开yun体育app官网网页登录入口，连接杆轴承和凸轮轴轴承。由于足够的润滑，这些轴承几乎没有摩擦损失，但是随着轴承直径的增加和旋转速度的增加，轴日志的圆周速度增加，运动部件的惯性力增加，并且损失的这一部分将会增加。
（ii）驱动配件的损失
这里提到的附件是指确保发动机运行的组件或组件，例如水泵（水冷发动机中的风扇），油泵，燃油喷射泵，电气分配器，速度调节器等；尽管有些不是每个人都需要进行发动机操作的必要组件，但除非另有说明，否则通常不包括发电机，用于汽车制动的空气压缩机，转向辅助泵等。有时规定，机械损耗不包括水冷发动机的空气过滤器，散热器和冷却风扇，必须根据特定情况或相关法规确定。
在一些两冲程发动机中，必须添加驾驶扫描泵的损失；在机械增压发动机中，必须添加增压器的损失。
附件消耗的功率随着发动机速度和润滑剂粘度的增加而增加。配件的功率损失占机械损失的一小部分。
（iii）泵气损失和空气阻力损失
泵气损耗是在入口和排气过程中消耗的功率。此外，它还包括活塞，连杆，曲轴等零件，这些零件在曲轴箱高速移动时被消耗掉以克服油雾，空气阻力和曲轴箱通风。该值很小，不能单独测量。
（iv）机械损失的份额
图1显示了通过几种不同的负载和速度下的1.6 L四缸天然吸气的汽油发动机和柴油发动机测量的主要机械损耗项的值的比较。可以看出：
①在各种情况下，机器零件的损失（活塞，曲柄连杆机构和凸轮轴系统）占最大份额（范围从50％到80％），柴油发动机的损耗比大于汽油发动机的损失率。
②配件的消耗通常不超过10％。由于燃油喷射泵高压，柴油发动机的损耗比大于汽油发动机。
③泵气损耗的比例差异很大，在5％至40％之间变化。当高负载低时，高速和汽油发动机会显着增加；负载对柴油发动机的影响很小。总体而言，低速泵和空气损失远高于柴油发动机的泵和空气损失。
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影响机械损失的因素
1。摩擦损失
在机械损失中，摩擦损失占最大比例。摩擦损失与诸如零件表面的润滑条件，相对运动速度等的因素有关，例如气缸壁和活塞环之间的摩擦，活塞的结构，裙子的几何形状，圆柱体diameter and stroke, etc. In order to reduce friction loss at the piston, a method can be adopted to reduce the number of piston rings, thin the piston thickness to reduce the inertia force and减少活塞裙的接触区域。 Reducing the weight of the parts and the reciprocating inertia force can reduce the load at the bearing, reducing the width and journal of the bearing to reduce wear.空气分布机理中阀门的摩擦与润滑条件和速度密切相关。由于飞溅润滑，当发动机速度较低时，空气分布机制的润滑较差。减少空气分配机构的运动部位的质量和使用辊轴承的使用可以减少摩擦和磨损。
2. Engine speed
After the engine speed increases (the average piston speed increases), all parts of mechanical loss increase significantly. As the speed increases, the relative speed of each friction surface increases, and the friction loss increases; the reciprocating inertia force of moving parts increases, and the mechanical loss increases; the loss of drive accessories and pump air both increase with the increase of rotation speed.从图2可以看出，旋转速度增加，机械功率损耗增加，机械效率降低。柴油发动机的摩擦损失大于汽油发动机。 This is caused by the high compression ratio, high cylinder pressure, and large mass of moving parts. Since the speed has such an important impact on mechanical losses, it has become an obstacle to strengthening the engine by increasing the speed.一。
3. load
The load of the engine usually refers to the engine's drag torque. In order to ensure the engine is running stably, when the resistance torque changes, it is necessary to adjust the engine torque, so the load can be represented by the torque output by the engine, and sometimes it is represented by power or its percentage. The increase in load means that the fuel supply per cycle increases for the diesel engine, and the gasoline engine means that the throttle opening increases and the inflation per cycle increases.
When the engine speed is constant, as the load decreases, the average indicator pressure pmi drops, while the average mechanical loss pressure pmm drops slightly, almost remains unchanged, as shown in Figure 3. This is due to the reduced load, the cylinder and piston temperature will drop, and the lubrication of the piston gap will improve. Moreover, the pressure in the cylinder also decreases, thereby reducing the friction between the piston and the bearing.但是，这种变化很小，n保持不变，泵气损失和驱动配件损失通常不变，因此PMMM随着负载而变化不大。
根据公式
可以看出，负载降低，机械效率降低。直到闲置，pe = 0，pm = pi，这表明所有功率都在机械损耗中消耗，因此ηm= 0。
4。润滑剂质量和冷却液温度
The viscosity of the lubricant directly affects the magnitude of friction loss.它具有较高的粘度和高摩擦力的损失，但其承载能力很强，并且很容易保持液体润滑状态。它具有低粘度kaiyun.ccm，良好的流动性，并且消耗了较少的摩擦功能，但承载能力较差，并且油膜容易破裂，并且完全失去了润滑。 The viscosity of lubricating oil is not only related to its variety and grade, but also affected by temperature. The temperature increases and the viscosity decreases. When choosing lubricating oil, lubricating oil with less viscosity should be selected based on the performance and usage conditions of the engine. On the premise of ensuring reliable lubrication, and the viscosity should be smaller as much as possible.
The temperature of the coolant directly affects the temperature of the lubricant, which also affects the magnitude of friction loss. The relationship between the mechanical loss power Pm and the lubricant oil temperature and the coolant temperature is shown in Figures 4 and 5. At a certain oil temperature, the Pm value is the smallest.
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Mechanical loss measurement method
1. Method of showing merit
For naturally aspirated engines, you can directly calculate the power process work on the power diagram to obtain the instruction work Wi. For supercharged engines, theoretical pump qigong is also required to obtain Wi. Wi is subtracted from the bench to measure it. The effective work obtained can be calculated by obtaining the mechanical loss work Wm and the mechanical efficiency ηm, including the pump gas loss. Furthermore, mechanical friction loss, accessories consumption and pump air loss can also be classified. Theoretically, this should be a direct and reliable method, but due to the following reasons, the motivation diagram method is only applicable to engine research and development work.
(1) Since the change in the pressure in the cylinder near the upper dead center is relatively gentle, the position of the upper dead center of the power diagram is not easy to accurately determine. A little error in the upper dead center position will cause a large error in the Wi-calculation value, because the work value corresponding to the deviation angle of the upper dead center happens to be positive and negative. Only by repeatedly calibrating precision instruments can satisfactory results be obtained.
(2) There is uneven working conditions of each cylinder of the multi-cylinder engine, which makes the pressures of each cylinder of the same cycle vary. Therefore, the pressure of each cylinder must be measured simultaneously to eliminate the inhomogeneity. Even in scientific research experiments, such strict requirements may not be met.
2. Inverted drag method (motor direct drag method)
在功率测功机的测试台上，首先根据测试条件将发动机运行到正常稳定状态。 After the water temperature, oil temperature and other indicators meet the normal requirements, quickly cut off the oil (diesel engine) or cut off the ignition (gasoline engine) and immediately Turn the dynamometer motor into a motor to run, and drag the engine backward以相同的速度。测得的反向阻力功率是发动机损失的机械功率。 Obviously, this measurement method has intake and exhaust gas flow, which will inevitably include the pump gas loss work in the mechanical loss work under test.此方法不可避免地会导致以下错误。
（1）在测量过程中，发动机处于非耐燃性状态。 On the one hand, the pressure in the cylinder is lower than the normal combustion pressure, and the gap between the piston and the cylinder liner increases due to the decrease in temperature, resulting in a decrease in mechanical friction loss; but on the other hand, the cylinder is The temperature is low, the viscosity of the lubricant increases, which increases friction loss.
(2) Due to the low working fluid temperature and increasing density, the exhaust pressure also increases, which increases the pump gas loss.
(3) For the repeated inverted drag cycles of compression and expansion, due to irreversible loss and heat transfer of the working fluid to the periphery, the closed negative work area where the compression and expansion lines shown in Figure 6 do not overlap. This consumption has been included in the normal cyclic power process work, and here it is obviously repeated calculation (of course there is a difference in numerical values), which increases the friction loss of the mechanical being tested.
上述因素可能会被抵消或相互叠加，从而使错误难以估计。由于汽油发动机的压缩比低，机械损耗的测量误差通常很小，而柴油发动机的测量误差很大。
3。气缸杀死方法
气缸减压方法仅用于多缸发动机。假设当N缸发动机正常运行时，测得的有效功率为PE。然后发动机的第i-th气缸已熄灭（停止点火或切割），并且以相同速度运行的（n-1）气缸的有效功率被测量为（pe） - i。 At this time, it can be approximately believed that the total mechanical loss power Pm has not changed, so the reduced output power after the cylinder is extinguished is the indicated power of the i-th cylinder Pii, that is, Pii = Pe − ( pe） - i（1）是因为pm = pi -pe，并且
Substitute the above formula to get
（2）
Using formula (2), you only need to measure the Pe of the whole machine and the N-order power (Pe) − i of the cylinder in turn, and then you can calculate the mechanical loss power Pm. This method is simple and feasible, without any additional testing equipment or motor back-drag, so it has been widely used.
It should be pointed out that the method of destroying the cylinder is still an inverted drag method in essence, but it is just a power of the "N-1" cylinder to drag the destroyed cylinder backwards. Therefore, the deviations of the theoretical backward drag method will appear in the cylinder destruction method. However, since the entire machine state during the cylinder-destroying method is closer to the real operating state, some errors will be relatively small. But there are still the following situations that will lead to new errors.
（1）擦掉多缸发动机后，入口和排气系统的压力波（主要是指汽油发动机）的动态效应将影响每个气缸的入口和排气的分布均匀性，从而导致additional measurement errors.
（2）从误差理论的角度来看，公式（1）是两个大数字PE和（PE） - I具有相似值的减法，这将增加PII的误差。
4。燃油消耗线方法
当发动机速度保持不变时，如图7所示，整个发动机燃油消耗速率的变化曲线（有效的平均压力PME）。然后将这条线扩展到与水平坐标PME相交的点A coordinate is
The value represented is the average mechanical loss pressure Pmm required.
当图中的水平坐标为正时，相应的测量点都是输出功率点；对应于PME的相应点B为0是空闲点。当PME负面时kaiyun全站网页版登录，当外部输入功率但发动机不会关闭阻力点时，它是相反的，而点A是发动机停止并且不消耗燃料的完整阻力点，因此
The value represented is the average mechanical loss pressure Pmm obtained by back-dragging, which obviously also includes pump gas loss.
The accuracy of the fuel consumption line method depends on whether the true law of the curve can be found and fitted.柴油发动机中型和低负载部分的燃油消耗曲线接近直线，并且整个汽油发动机的燃料消耗率与负载（PME）不成比例，因此燃料消耗线不适用to gasoline engines.
By summarizing the last three methods above, the following conclusions can be drawn.
(1) The inverted drag method is only suitable for use on test benches with electric dynamometers. Since high torque electric dynamometers are expensive and rarely used, it is generally difficult to use the reverse drag method for medium and large diesel engines.由于汽油发动机的扭矩很小，因此很容易满足向后的阻力测试条件。另外，压缩相对较小，因此经常使用向后的阻力方法。 Gasoline engines rarely use the cylinder extinguishing method, not only because there is interference from inlet and exhaust after the cylinder is extinguished, but also because one cylinder extinguishes the fire, which poses a safety hazard.
（2）小型柴油发动机可用于杀死气缸或反向阻力。注意使用过程中测试的准确性。 The fuel consumption line rule is mostly used in the production and debugging of naturally aspirated engines as a means of product quality monitoring.
(3) The turbocharged engine cannot use the reverse towing method and the cylinder decompression method because they both destroy the normal operation of the supercharged system.燃油消耗线方法也仅在低升压下（PB
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相关条目
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参考
总编辑王·温比奥（Wang Wenbiao）。第14章：1000个有关泵和风扇单元的集中控制技术的问题。中国电力出版社，2005年4月，第一版。总编辑汉汤昆。第3章：实际发动机周期和评估指数发动机原理。由南中国中国技术学会出版，2010年。08。 Gao Han，Jiang Xiao，编辑。 Chapter 2. Engine performance indicators and engine principles. Beijing Jiaotong University Press, 2007.12. Edited by Wang Jianxin, Shuai Shijin. Chapter 3. Work cycle and energy utilization principles of automobile engines. Tsinghua大学出版社，2011.03。
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