windscreen wiper

A windscreen wiper is a motorized mechanism that removes rain, snow, dust, and debris from vehicle glass using a spring-loaded rubber blade dragged across the surface. The blade sits in a metal or plastic frame attached to an arm that pivots from a gearbox mounted above or below the windscreen. Modern vehicles typically have two wipers on the front windscreen operating in tandem, synchronized to meet at the center, plus a rear wiper on hatchbacks and SUVs. Older systems used a single wiper; some large vehicles use three across the front.

The rubber blade, called the wiper element or blade refill, is the wearing part replaced every six months to three years depending on climate and use. Common blade lengths are 550mm to 700mm on passenger cars. The blade must maintain even pressure across its width to avoid streaking and chattering. Pressure comes from a spring mechanism in the arm assembly; too much pressure causes rapid blade wear, too little leaves wet patches. The blade angle relative to the glass is critical: modern designs use a slight curve or a spoiler to maintain contact at highway speeds where air pressure tries to lift the blade.

The motor driving the wiper is usually a small electric motor with a worm gear that converts rotational motion into the side-to-side pivoting motion of the arm. Wiper motors typically run on 12V DC (24V on heavy trucks and equipment) and draw 3 to 8 amps depending on blade resistance and speed setting. Most vehicles have two or three speed settings plus an intermittent mode that cycles the wipers at adjustable intervals, useful in light drizzle. The motor is protected by a thermal cutout that stops the motor if it jams or is overwhelmed by ice.

Wipers fail by blade degradation, rubber cracking and hardening in sunlight and ozone, loss of pressure from worn springs, or separation of the blade from its frame. Motor burnout occurs from overload (frozen wipers in winter, excessive debris on glass) or corrosion of electrical contacts. The pivot arms can seize from rust or from ice buildup between the arm and the windscreen frame. Electrical issues include blown fuses, loose connectors, or failure of the control stalk on the steering column that selects speed and intermittent function.

Windscreen wipers are mandated safety equipment in most jurisdictions; visibility standards typically require that a wiper system clear a minimum rectangular zone of the windscreen within four seconds. The term "windscreen" is British English; American equipment uses "windshield" but the device remains unchanged. Industrial equipment, heavy trucks, and specialist vehicles use the same basic principle but with heavier-duty motors, larger blades, and sometimes supplementary wash jets that spray cleaning fluid onto the glass ahead of the wiper blade.