PH Origins: Rain-sensing wipers

How aircraft icing and rain-soaked convertibles led to automatic wiper systems

Water, should it get somewhere it isn't meant to be, can cause all manner of grief. Should water get into a fuel tank, it can cause corrosion, poor running and component damage. Water in carpets can cause the fibres to delaminate from the backing and, over time, result in the formation of harmful mould and fungi. Then there are the water-related issues of structural rust, paint damage, wood rot and more.

Detecting water in critical areas can be problematic, though; water running from a burst pipe between two walls, for example, may cause all manner of havoc and not be obvious until it soaks all the way through to the surface.

By the mid-1800s, inventors had come up with ways to detect water levels and cracks in pipes remotely; such systems were critical for safely operating high-pressure steam boilers and often relied on straightforward float-based level sensors. As technology advanced, engineers then began developing sensors that would react directly to moisture or water when it touched the sensor itself.

Detroit-based engineer John Roby, among others, came up with a 'sensor' in 1914 which contained a chemical that reacted with water; when falling rain hit the chemical 'sensing' element, the reaction would cause a small string to start burning. When the string broke, it would trip a switch and sound an alarm.

A similar one-time system, using salt that would conduct when wet and complete an electrical circuit, was developed by inventor Benjamin Roodhouse in 1926. 'My device is intended to be placed at joints or other places where leaks may commence with a suitable electric circuit, or circuits, in which an alarm is included,' wrote Roodhouse in a patent submitted in 1926, 'so that the presence of the leak will be indicated at its inception.'

Soon, water-sensing devices that could be used repeatedly arrived - such as those using reeds that would bend under the weight of contacts when moistened, completing a circuit. It wasn't long before innovative ways to use these new sensors began appearing.

General Motors was among the companies exploring the use of water sensors but, in 1934, their usage was intended for automatically controlling the actuation of windows in buildings. The sensors, which would close windows automatically when rain started falling, were part of an overarching building control system - which also featured auto-closing light shades.

John Anderson, who founded The Anderson Company in 1918 - and later established ANCO, the renowned wiper blade manufacturer - was seemingly the first to propose the use of such technology for vehicles. Anderson's concept, due to the war efforts at the time, was focused on aircraft; in particular, he wanted a system that would automatically prevent the build-up of ice on the windshield.

ln aircraft, a special problem arises since the greater portion of the flight may be performed by blind or instrument flying, and it may be only when the craft is in the vicinity of the objective that the pilot has occasion to look through the windshield,' wrote Anderson in 1942.

If at the time that the objective has been nearly reached, the windshield is obscured by a film or sheet of foreign matter such as frost or ice, it will be apparent that it may take considerable time for a windshield wiper to remove the frost or ice to provide clear vision.'

To resolve this issue, and keep the screen clear without requiring any observation or input from the pilot, Anderson designed a system that featured a series of electrodes on the screen. When ice began accumulating on the screen, the resistance between the conductive elements would change - triggering relays which would operate the wipers and a de-icing fluid spray.

Anderson also noted that rain could cause the system to function, so care would have to be taken to calibrate it to avoid unnecessary operation and wasting of the defrosting fluid. The penny then seemingly dropped that such a conductive sensor set-up, which would be reliable and easy to maintain, could be ideal for use in cars - and a flurry of patents followed.

Surprisingly, though, none focused on the process of automating wiper operation. Instead, as was the case with GM's earlier building-related patent, inventors set about using conductive rain sensors to automatically close the windows of cars.

Electrical engineer Hugh Nutter, who had served in the US Navy and worked for General Electric, was among those who patented such systems. 'One of the objections to the use of so-called convertible automobiles has arisen from the fact that a sudden rain or snow-storm will thoroughly drench the interior of the automobile while the owner is absent and while the top is down,' stated Nutter in a 1949 patent application.

The present invention solves this prior problem by providing an electrical system which will automatically cause the top to be raised and optionally also the windows of an automobile upon the occurrence of rainfall, without the need for any action on the part of the operator or even for his presence.'

A practical demonstration of this configuration subsequently made its debut in GM's 1951 LeSabre concept car. The car's styling echoed the cutting-edge jet aircraft of the day and, unsurprisingly, the ever forward-thinking GM had crammed a plethora of advanced technology into it; it had a supercharged 3.5-litre V8 that could run on methanol, a rear-mounted transmission, heated seats, integral jacks and a 12-volt electrical system.

The futuristic convertible also featured a rain sensor in the centre console, which functioned in the exact fashion as the set-up described previously by Nutter. If the car was parked and a drop of rain hit the sensor panel, the top would automatically raise and the windows would close. GM would later make this system available as a dealer-fitted option for 1955 Chevrolets and, in 1958, it would reach production in the Cadillac Eldorado Biarritz convertible.

As customer demand for creature comforts such as cruise control increased, and safety became more important, companies began exploring other areas in which to deploy new technology. By 1968, companies such as Ford were extending on the concept with wiper energisation systems that featured conductive assemblies on the windscreen - which, in Ford's case at least, referenced Nutter's earlier sensing and triggering patent.

Japanese manufacturers had also started researching automatic wiper controls; Nippon Denso, in late 1968, also patented a system that could automatically stop and start a car's windscreen wipers. As the company outlined in its design documents, the system would 'stop its wiping operation automatically when the rain has finished and therefore will not bother the driver and is highly advantageous from the standpoint of safe driving.'

Citroen then took the first step towards producing an automatic system in its flagship SM, in March 1970, by introducing automatically adjusting intermittent wipers - but did away with the need for any external sensors, which could get damaged or dirty, with a neat piece of electrical engineering.

When the driver put the wipers into the intermittent mode, the system would monitor the current draw of the wiper motor. If the current draw was high, it would indicate that the screen was dry and that the blades were dragging on the glass. The Citroen's wiper system would react to this by parking the wipers for a moment; this would allow for more rain to build up on the screen, allowing for smooth wiper operation when sweeping resumed.

Nissan followed with a similar system, which arrived on the market in June 1983 in the Cedric, 300ZX and Skyline. Judging by patents from the era, Nissan made use of a piezoelectric element-based sensing system that responded to the vibration produced by rain falling on the car's body; if the wipers were set to intermittent, the interval between sweeps would be adjusted to suit the rainfall.

Taking the final step fell to General Motors which, in 1996, unveiled the first automatic system. 'Rainsense', when engaged by putting the wipers in automatic mode, would turn on the wipers when rainfall was detected and adjust the interval as required.

Unlike preceding systems, Rainsense relied on LEDs that shone into the windscreen and measured the degree of refraction; variations in the light returned could be used to judge the amount of water on the glass and alter the wipers' behaviour. This system, based on the principle of total internal reflection, was soon adopted by others and is now a common feature in modern cars.

These rain-sensing wiper systems, along with concepts such as hill-hold assist and auto-dipping lights, serve to cut hassle and reduce the chance of accidents - and, today, manufacturers continue to strive to further automate the process of driving itself, using techniques ranging from adaptive cruise control through to semi-autonomous driving systems.