【作者】 余柏林；

【导师】 徐静平； 刘胜；

【作者基本信息】 华中科技大学 ， 微电子学与固体电子学， 2008， 博士

【摘要】 发动机电子控制燃油喷射系统的关键技术,是对发动机的空气进气量的准确测量,使得空气进气量与喷油量处于最佳比例。在车用空气流传感器中,由于热式流量传感器具有无机械传动,无需压力补偿,响应速度快,测试灵敏度高等优点。因此,热式空气流量传感器发展非常迅速,且在汽车领域开始得到广泛的应用。本文中研究的空气流量计为温差热膜式流量传感器。其主要内容如下:由于进气管中空气流速范围与热膜式流量传感器测试量程不匹配,并且在进气管中的空气流动状态为湍流,不能满足温差热膜式流量传感器的测试条件。研究中通过在内燃机进气管中设置取样流道,测试取样流道中的流速,间接反映进气管中空气质量流量。通过取样流道中的结构参数设计,可控制测试段的流速,使其满足温差流量传感器的测试流量要求。同时使整个流速范围内测试段保持层流。研究了传统热膜式流量传感器,通过商业软件对流量传感器在各种状态下的温度分布、测试范围和测试精度进行了模拟,得到了较为合理的测试电阻的位置及其布局和芯片的结构。其可测流速范围为0-5m/s。采用半导体工艺研制出了温差横膈膜式流量传感器芯片,控制电路和信号输出电路分别为两组惠斯通电桥,分别为保证加热电阻的加热温度和测试电阻信号输出。通过测试分析初步验证了理论分析的正确性。并在内燃机的进气质量流量为8～370Kg/h时,得到放大后信号电压为0V～3.1V,并且呈现很好的单调性。分析了加热电阻的温度和宽度对测试精度和测试范围的影响。本文中还针对带有横膈的膜热膜式流量传感器的测试范围较窄的问题,提出二次差分的测试方法,该方法大大扩大了流量的测试范围,但同时降低了其测试精度。提出了一种基于玻璃的流量传感器,由于玻璃的热导率较小,不需要构造横膈膜或隔热桥,可直接在玻璃衬底上溅射薄膜电阻,因此,该传感器具有制备工艺简单和耐流体冲击能力强的优点。但是其工作功耗大,测试精度也相应的降低。采用流体软件模拟了各种情况下的温度场,得到内燃机进气管的质量流量与输出信号电压的关系。在实验上验证了模拟趋势的正确性,确认该模拟具有一定实践指导性。芯片的流速测试范围可达到10m/s,在内燃机的进气质量流量为8～370Kg/h时,输出电压为0V～1.4V。创新性的提出了一种新颖的集成微沟道流量传感器,通过微沟道的导向作用,达到增加横膈膜上的强迫对流换热效果,从而提高传感器的测试精度。通过降低取样流道中的流速与内燃机进气管中的流速比,实现降低流体的击波压力,且保证了测试精度。模拟了流量传感器在各种状态下的温度分布、测试范围和测试精度,得到了理想的电阻布局方式和芯片结构。与传统热膜式流量传感器相比,其最大信号输出提高了25%,在内燃机的进气质量流量为370Kg/h时,输出信号电压可以达到3.86V。但其测试范围有一定程度的缩小,其芯片表面最大测试流速为3m/s。分析了各种流量传感器在测试过程中的动态特征。内燃机进气管中的流动处于非稳定状态,呈周期型变化。本文中模拟了正负阶跃脉冲气流下三种传感器的延迟特性。非稳态流动中,影响传感器响应时间的主要因素为流场稳定分布的延迟时间、衬底(或者横膈膜)热平衡分布的延迟时间和加热电阻温度补偿延迟时间。在正阶跃脉冲气流下,三种传感器的响应时间分别1.4ms,2.5ms和1.2ms。在负阶跃脉冲气流下,三种传感器的响应时间分别1.5ms,2.5ms和1.5ms。研究了环境温度对流量传感器的输出电压信号的影响。随着环境温度的增加,电压信号明显减弱,这会给流量计中作过程中带来很大的误差。随着环境温度的降低其饱和现象越显著,甚至影响到传感器的测试量程。本文中提出了环境温度的补偿方案,在传感器芯片最上游放置一根环境温度测试电阻R_k,通过电路控制使得加热电阻与进口空气之间的温差保持恒定值。通过模拟得到信号输出电压的误差大大减小,但不能完全避免误差。这是因为随着温度升高,流体的热导率越高,强迫对流越大,固体热导率小,导致信号电压越大。更多还原

【Abstract】 The key to Electronic Fuel Injection System of automobile engine is the accurate measurement of air mass flux in manifold in order to maintain an optimal air-fuel ratio. For many air flow meters, the thermal film based air flow meter develops very rapidly and begins to be applied to automobile widely, due to its many advantages such as no mechanical transmission, no pressure compensation, quick response and high sensitivity. In this thesis, the main object of this study is the temperature difference thermal film based flow sensor. The main research contents of this thesis are as follows:Due to the fact that the air flow velocity range in manifold is inconsistent with the measurement range of thermal film flow sensor, and the flow condition in manifold is turbulent, which does not meet the measurement conditions of the thermal flow sensor. An especially small sampling channel is designed inside the manifold in this research, so that the laminar flow condition can be maintained throughout the measurement range in the small sampling channel. Through measurement of flow velocity in small sampling channel, the air mass flux in manifold can be obtained. By adjusting the structure parameter of small sampling channel, the flow velocity range in small sampling channel is maintained to be consistent with the measurement range of thermal film flow sensor.The traditional thermal film flow sensor is studied. Extensive CFD simulations using the software package FLUENT are performed throughout the design process, and the temperature distribution, measurement range and measurement precision are obtained. The optimal resistor layouts and structure parameter are obtained. The maximal measurable velocity is 5m/s. The temperature difference membrane flow sensor chip is fabricated by semiconductor technology. The heater temperature is maintained at a constants temperature by a Wheatstone bridge with the heater resistor as a bridge arm, and signal voltage is obtained by another Wheatstone bridge. The simulation is verified to be appropriate by experiment. When the air mass flux in manifold is 8-370 kg/h, the output signal voltage is 0V-3.1V after magnification. The effect of heater temperature and heater width on measurement precision and measurement range is investigated. In this study, a second difference scheme for the temperature is proposed. The maximal measurement range is broden largely, but the measurement precision decreases remarkably.A type of flow sensor based on glass substrate is proposed. Due to the low thermal conductivity of glass, the membrane does not need to be structured. Therefore the fabrication technology is simple, and it can work under large fluid press. On the other hand, the consumption of this flow sensor is large, and the measurement precision is low. The temperature field is simulated by software FLUENT under different conditions, and the temperature difference is calculated for different positions on the glass surface, the relationship of output signal voltage and income mass flux is obtained. The flow sensor based on glass is fabricated by semiconductor technology, and all of this simulation is verified to be correct. The maximal measurable velocity can reach 10m/s. When the intake air mass flux is 8～370Kg/h, the signal voltage is 0V-1.4V.A new type of novel flow sensor integrated with a micro channel is proposed. The uniqueness of this flow sensor is that there is thermal convection effect on both sides of diaphragm by flow guide of a micro channel, which results in a more sensitive temperature distribution. The temperature characteristics of the novel flow sensor are simulated at different flow rates, and the optimization positions of the test resistor pair on the membrane are obtained from the simulations. Compared with traditional flow sensors, this flow sensor has higher measurement precision, and the maximum output signal voltage improves 25%. When the air mass flux in manifold is 370 kg/h, the highest signal voltage is 3.86V. However, the measurement range is narrower than that of traditional flow sensor, and the maximal measurable velocity is 3m/s.Dynamic response properties of all types of flow sensors are studied. In the manifold of engine, flow is unsteady and periodical variety. The dynamic properties of three flow sensors have been simulated, and the main effects of dynamic response are the times of flow field and temperature field achieving a balance and heater temperature compensation time. Under positive step pulse flow, the response times are 1.4ms, 2.5ms and 1.2ms respectively for three flow sensors, and under negative step pulse flow, the response times are 1.5ms, 2.5ms and 1.5ms respectively for three flow sensors.The effects of ambient temperature on measurement signal of flow sensors are studied. With ambient temperature increasing, signal voltage of flow sensors decrease remarkably, which will bring a lager deviation. With ambient temperature decreasing, the saturation effect of temperature difference becomes more remarkable, and the measurement range becomes narrower. In this research, an ambient temperature compensation method is proposed. On the front of flow chip, ambient temperature is tested by a resistor R_k, and it is connected to Wheatstone bridge as a part of bridge arm. A constant temperature difference is maintained between heater temperature and ambience temperature. After this the signal deviations of flow sensor is decreased largely. There is still a small deviation, due to the material parameter varying with ambient temperature varying.更多还原