Vehicle Safety Systems

Vehicle Safety Systems

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由Christine Graham，Systems Engineer

Seat Position Sensing

图1.前端和侧面冲击气囊需要座椅和乘员位置的精确数据。

乘员安全是汽车设计中最关键的元素之一。因此，安全系统继续变得更加复杂，以限制，并最终在事故发生时造成人身伤害。

在安全系统中使用座椅位置感测，以确定乘员与方向盘相对于方向盘的位置，防止气囊展开有过大的力。

The most common solution today incorporates two-wire, unipolar, Hall-effect switches in sensing discrete seat position zones. The sensor IC must relay this information in the form of a digital output to the controller unit indicating a particular zone. This information must be correct at start up of the vehicle, so the sensor IC output must decode without any user action.

The seat track is typically a ferrous metal material capable of interrupting the magnetic field between the Hall-effect sensor IC and a magnet. The ferrous metal of the seat track passes between the switch and the magnet causing the switch to turn on or off, relaying seat position information to the controller unit. A change in the output state of the sensor IC indicates to the controller unit that the seat has passed into a particular zone.

根据每个座椅轨道的两个传感器IC，可以使用任何数量的区域，这取决于使用多少霍尔效应传感器IC，可以使用四个区域。由霍尔传感器IC提供的信息由控制器处理，以确定相对于方向盘的座椅位置。在方向盘上的一个更近的区域中的座椅将向控制器单元指示较低力部署是必要的。位于方向盘最远的后部区域中的座椅位置需要较高的力部署。控制器单元对霍尔效应传感器IC的输出状态进行解码，以确定座椅定位的区域。两个传感器IC将提供方便的灰码输出，如图2所示和下表。

Figure 2. Position sensor ICs relay proper seat location to the controller unit the entire time the vehicle is on. Occupants are unaware of the fact that the vehicle is making life or death decisions automatically with no user interface required.

The vast selection of Hall-effect sensor ICs allows different solutions for the same application. A higher resolution may be required to determine exactly where the seat is at all times. The highest resolution solution is to use a linear, analog Hall sensor IC, which produces a voltage output proportional to the strength of the magnetic field. A dual pole magnet in a slide-by configuration with the linear will produce an output ranging from 0 volts to 5 volts with the proper design.

Hall-effect technology is highly reliable and relatively inexpensive. If automatic sensing is required the solution must be dependable.

如果需要更高的精度，可提供可编程开关和线性设备，可以通过允许线路编程来最小化堆叠公差。

使用back-biase亚铁目标能被探测到d Hall-effect sensor IC. These sensor ICs incorporate a Hall circuit and rare-earth pellet in one overmolded assembly. Back-biased solutions are offered for switch and linear designs. These assemblies simplify manufacturing and offer an optimized electrical and magnetic design in a single overmolded package.

安全带扣感应

Save皮带扣，SBB是霍尔效应技术已被用作安全系统的一部分的另一个区域。双线，单极交换机再次是一个简单，但可靠的解决方案，该解决方案对于今天的许多汽车通用。霍尔效应装置（HED）的目的是保证扣扣的适当锁定，从而确保乘员在事故或突然停止时被适当地限制。

Similar to the seat position sensing application, seat belt buckle switches operate using a vane interrupt concept. In this case the buckle, made of a ferrous material, is responsible for interrupting the magnetic field between a magnet and the Hall-effect device. Typically when the field is interrupted, the device output switches on and when the buckle is removed the device switches off. This information is sent to the controller, which then processes the data in conjunction with data from the seat position sensor IC and other outputs in order to reliably deploy air bags in the event of an accident.

申请障碍

• SBB传感器IC具有紧密的空间限制，使得使用印刷电路板难以。因此，将互连线焊接到铰接导线是更常见的方法，作为封装过程的一部分，以最小化尺寸。然而，焊接到引线采用焊接专业知识，并且通常在焊接设施中收缩。焊接霍尔效应装置中最常见的误差之一是允许到达IC的过度的热/电源，导致线键遭到灾难性损坏。新的焊接过程中看到的另一个常见错误是引线的夹紧不足，允许导致在与焊接尖端接触期间扭转或拉动。这也将对导线键造成灾难性的损坏。

除了空间约束之外，传感器IC经受高ESD水平并导致磁干扰：

• customer-accessible points within the vehicle, such as the tongue of the buckle assembly,
• shunting effects, on the magnetic field, to the sensor IC due to the ferrous properties of the buckle assembly, and
• 机械扣组件的宽公差，导致撞击霍尔效应传感器IC的磁场的大变化。

Choosing the right sensor IC is critical to meeting all the application requirements.

Application Solutions

图3.安全带扣的典型机械组件，显示与霍尔效应传感器IC的电气连接。

• Transient/ESD protection has been accomplished with the use of a 0.1 µF bypass capacitor welded between sensor IC supply and sensor IC ground. In the case of a PCB, an MOV has been used in addition to the bypass capacitor to protect the sensor IC against harsh EMC/ESD conditions due to the use of a chassis ground.当传感器IC对EMC / ESD稳健时，旁路电容器可能是足够的。
• A sufficiently large magnet is required to overcome the shunting effect caused by the buckle assembly itself. SmCo and Neodymium are common magnet materials used in Seat Belt Buckle applications. They provide large field levels to compensate for the mechanical tolerances and possibly large air gaps > 3 mm) seen in SBB applications.
• 机械组件的公差可以在撞击传感器IC上的现场水平中引起大的高斯变化（数百个高斯）;因此，必须表征所有条件，以确保传感器IC切勿切换到不正确的状态。不得导致霍尔效应传感器IC的错误切换的条件如下：
  • 用舌头到位正常弯曲位置。
  • Normal unbuckled position with the tongue removed.
  • 当被坐在它上的人或坐在扣上的人座上坐在扣组件上时，舌头过度旅行。
  • False latch condition when something other than the actual tongue is pushed in, holding the buckle in a falsely latched condition (popsicle stick, toy, etc).

  Suggested Devices

  Allegro™ 零件号	Temperature Range	包装类型	Tape & Reel 可用
  A115x.	EL	LH, UA	Yes
  A119x	E, L	LH, UA	Yes