Automotive Glass and Its Role in Vehicle Safety - The Second Edition
In a previous analysis, we said that there’s more to a modern windscreen than meets the eye. A windscreen today is a core component that forms part of the structural frame and integrity of your vehicle, which will help prevent the roof from collapsing or caving in should the vehicle be overturned in an accident situation.
Secondly, we spoke about the fact that windscreens also act as a shield to road debris and other flying objects from penetrating through the glass and in case the glass is damaged or cracked in these types of situations, your windscreen will not break into large shards of glass that will pose a safety threat to you or any of your passengers inside the vehicle.
The function of a windscreen does not end there and in today’s edition, we take a closer look at more safety functions that are found in the form of sensors mounted on modern windscreens today.
Today, safety is enhanced through a number of safety sensors otherwise known as driver assist systems that are often incorporated through different types of sensors that are placed on the windscreen of your vehicle.
Below is a list of sensors found on your windscreen, their functionality and how they operate.
Assists the driver in rainy and stormy weather conditions by automatically switching the wipers on and off as well as controlling the speed of the wipers.
How it works:
The sensor is normally located behind the rear-view mirror on the glass (inside of the windscreen) and shines an infrared beam at an angle to the glass (usually 45 degrees). The reflection of the beam is then measured as a dry glass surface will reflect more of the infrared beam back to the sensor than a wet glass surface. By calibrating the sensitivity of the sensor correctly, a reliable trigger can be provided for the windscreen wipers. Obviously, the wipers also wipe the piece of glass covering the sensor so that it can determine when it has stopped raining.
These sensors control the lights of your vehicle and as such enhance road safety by giving the driverless to do and keep more focus on the road. It adds to the safety of other vehicles if the driver is a person who often forgets to turn on their lights when the sun starts to set, as it makes the vehicle visible to others around it.
How it works:
Vehicles with automatic headlights have an ambient light sensor that measures the level of ambient light. The sensor itself usually employs a photo-electric element as a trigger and is located close to the windscreen on the inside of the cabin (it can be part of the rain sensor unit). The sensitivity again needs to be calibrated and there would also be a time delay programmed between switching on and off (hysteresis) to prevent flickering of the headlights.
Lane Departure Warning System
This safety system is extremely helpful for drivers travelling long distances as it detects when a driver is moving over from one lane to another and then signals the driver by means of vibrating car seats and red lights flashing on the dashboard. If a driver were to get tired and snooze off on the long road, the vibration of the seats will wake the driver and as such help to avoid a possibly dangerous situation.
How it works:
This is more a system than a single sensor. It usually consists of a video camera mounted behind the rearview mirror of a vehicle (can be part of the rain and light-sensing unit) that records a view of the road ahead including the road markings. Clever software can then recognize the lane markings (sometimes also signs like speed limits) and determine the relative placement of the vehicle to the markings. When the system determines that the vehicle will cross a line marking either side of the vehicle unintentionally (indicator not switched on), the driver can be visually, audibly or through vibration be alerted to the situation. Modern systems also have the capability to return the vehicle to the lane if no action is taken by the driver by gentle steering or applying braking to wheels on one side of the vehicle in order to change direction slightly.
This sensor will assist in clearing a fogged-up windscreen in order to enhance driver visibility.
How it works:
To defog the inside of the glass in a vehicle, cabin automakers use the existing HVAC system combined with resistive wires in the glass if fitted. The most effective way to clear moisture is to employ heat, airflow and dry air. Therefore the aircon is used to dry the air before it is heated up and directed to the glass via the blower outlets. The task of the resistive wires is to heat up the glass when electricity is passed through in order to speed up the process. Ford developed (and patented) the “QuickClear” system that runs a fine mesh of wires through the windscreen of a vehicle to help clear fog, ice and snow in colder climates. These fully heated windscreens can also be found on certain models of Landrovers, Volvos & Jaguars.
City Safety Sensor
This group of sensors are extremely helpful to drivers typically driving in urban areas at low speeds up to 50km/h. If a driver were to look down and traffic suddenly comes to a stop in front of them, this sensor will take over the braking system of the vehicle and bring the vehicle to a complete stop if needed. If vehicles in front of you were to slow down and you don’t slow down as well, these sensors will also apply enough braking to your vehicle to avoid a collision. These sensors don’t apply smooth braking as the idea is not to encourage the lack of driver attention but only to avoid an accident situation.
How it works:
City safe primary refers to autonomous emergency braking systems (AEB) that is capable of preventing a collision with an object or another vehicle if the driver fails to take action. Most automakers employ Lidar (laser sensor), radar and/or a camera to detect static objects in front of a vehicle. Lidar normally only functions at low speeds and short distances whereas radar can be used at high speeds and greater distances. Radar is also employed for adaptive cruise control where the following distance to the vehicle in front is kept constant. Detecting pedestrian and cyclists are tricky and cameras with clever software make this possible. Full ABS braking can be initiated by the system to prevent an accident so it is important that the calibration ensures no false detections.
Rearview mirrors that tint automatically when it detects a glare from behind and assist the driver by not being blinded during night-time driving.
How it works:
Cheaper vehicles still use a manual rearview mirror with a tab at the bottom to change the angle of the mirror to give a “day” and “night” setting. The glass of the manual mirror is not of equal thickness when viewed from the side but thicker at the top than the bottom. Therefore during the “day” setting the main reflection of the reflective material of the mirror shows you the view behind and the faint reflection of the glass surface will show you the rear seats. When flipping the mirror to the “night” setting, this faint reflection will become your main view with the reflective material facing the roof’s headliner, which is black during nighttime. The modern equivalent is the electrochromic mirror which uses an electrical charge to change the reflective properties of the glass covering the reflective material (a chemical named tungsten trioxide is used as the active ingredient). It will have a sensor detecting incoming light and if it determines that is above a certain limit (like the headlights of an approaching vehicle at the rear) it will tint the glass and lessen the reflection to the driver.
From the examples mentioned above, it is clear that vehicle manufactures have put more focus on vehicle safety and driver comfortability in the last 20+ years and this ultimately contributes toward overall vehicle safety for all road users.
With all these added safety sensors to vehicles today, it is once again of utmost importance that windscreens are repaired or replaced by expert technicians to ensure that it is fitted correctly. Also, advanced driver assists systems such as those discussed above need to be calibrated by expert technicians in approved fitment centres with high-quality calibration equipment and expensive up-to-date software after a windscreen fitment has been done. Failing to properly calibrate these sensors will cause them not to function properly and void the reason for their existence.