Patent GB-1182681-A (GB)
Title: Vehicle windshield wiping system
Inventor: KEARNS ROBERT W
IPC: B60S1/48
Filed: 1967-02-13
Abstract: 1,182,681. Windscreen wipers. A. TANNER, E. CHOSID, L. TANN, D. TANN, G. TANN and H. TANN [trading as TANN CO.]. 13 Feb., 1967, No. 6693/67, Heading A4F. [Also in Divisions H1 and H2] A D.C. motor 22 drives a windshield wiper and is controlled by a printed circuit card 32 associated with wiper contacts which are driven by the motor. A selector switch having three-position contacts S1-S5 enables the motor to be pulsed to operate continuously at a speed determined by wiper arm WA whose position is adjusted by a ring of the selector switch. In another position of the selector switch the motor is energised intermittently to actuate the wiper blades through a complete cycle with a predetermined dwell period between cycles. The length of the dwell period is determined by the position of the arm WA. However, if the windshield is wet, the dwell periods are skipped for continuous operation of the blades until the moisture falls below a value determined by the setting of wiper WB. For pulse-control of the motor, ring r1 co-operates with rings r2, r3, to form a vibrating switch serving as a square wave oscillator. When rings r1, r2, are interconnected, base current for transistor Q1 flows into capacitor C1 as well as through resistor R2 are potentiometer P1. As the motor continues to turn, rings r1, r2, are disconnected but capacitor C1 retains its charge and the motor is still energised. When rings r1, r3, are interconnected, transistors Q1, Q2, are turned off and the motor is de-energised but continues to rotate. Capacitor C1 discharges through resistor R2 and potentiometer P1, the "of" period of the motor being determined by the setting of the potentiometer. When the capacitor is discharged, the motor again receives power although the wiper may still engage the ring r3, the capacitor being afterwards re-charged by connecting ring r1 to a conductive segment on ring r2. If the motor tends to slow down due to increased load, the percentage of time that the motor is energised relative to the "off" periods will increase. In the intermittent mode of operation, each wiping cycle is divided into full-torque, and controlled-torque regions, as well as a region designated by the angle O on the printed card. For full-torque on the upstroke, the transistors are shunted and the motor is connected directly to the supply, the ring r6 being co-extensive with the fulltorque region. During the controlled torque region, at the beginning of the downstroke, the motor is pulsed as before but its speed is determined by the position of wiper WB. At the beginning of the O region, the transistors are turned off and the wiper blades coast and may come to rest in the O region. The motor is de-energised for a number of successive dwell periods dependant upon the number of conductive segments on the ring r3 which lie between the position at which the motor coasted to rest and the end of the O region. The more moisture on the windshield, the further the blades will coast so as to require fewer steps to leave the O region. Under these circumstances, the total dwell time is relatively short and the frequency of wiping strokes is high to keep the windshield clear. Each dwell period is determined by the network C2, R2, P1, it being possible for the wiper blades to coast through the O region and enter the fulltorque region without stopping when the moisture exceeds a threshold value. In another arrangement, the transistor Q2 is dispensed with and the potentiometer P1 is replaced by a tapped resistor. When the selector switch is returned to the "off" position, the motor is stopped by shortcircuiting its armature through ring r7. The printed circuit card may be modified so that the transistors are removed from circuit when full torque is applied immediately after stopping, so protecting the transistors against overload. The resistance element of a potentiometer may be mounted on the printed circuit card to establish the dwell periods between cycles of operation of the wiper blades.