Abstract:
Windshield wiping systems commonly include a parking control, which delivers power to a wiping motor, while waiting for the wipers to reach a parked position. When the wipers park, the parking control terminates power to the motor. 
     The invention repeatedly exercises the parking control, in order to obtain intermittent wiper operation. That is, the invention allows parking to occur, and then waits for a short time. Next, the invention withdraws a wiper from parked status, and then allows the parking system to park again, and so on.

Description:
The invention concerns a control for a windshield wiper, which runs the wiper intermittently. 
     BACKGROUND OF THE INVENTION 
     Windshield Wipers are Parked When Not in Use 
     Many prior-art windshield wipers include a parking system, which parks the wipers, and then terminates power to the wiper motor. A generalized wiper will be illustrated, followed by a simplified, generalized parking system. 
     Simplified Example of Wiper 
     FIG. 1A illustrates a windshield wiper. A crank C, driven by a motor (not shown) rotates, as indicated by the arrow. The crank C drives a linkage L which causes a wiper ARM to reciprocate about a PIVOT between the positions shown in FIGS. 1A and 1B. (Modern wiper systems are significantly more complex than FIGS. 1A and 1B indicate, but the principles of these Figures nevertheless are applicable.) 
     When the wiper is not in use, the ARM resides in the parked position of FIG.  1 A. However, the ARM is not placed into the parked position by intentional manipulation by the driver of the vehicle. One reason is that, during wiping, the ARM is moving, and the ARM-motor-linkage system has inertia. To stop the moving ARM in the parked position, the driver must stop the motor at exactly the proper time, and let the wiper coast, by inertia, into the parked position. This task would distract the driver from his driving responsibilities. Consequently, electronic circuits have been developed which perform the parking task. 
     One Way to Park 
     In a simplified sense, the parking circuit utilizes a limit switch SW, shown in FIG.  2 . When the ARM resides in the parked position, the limit switch SW is closed, as in FIG.  2 . When the ARM resides in its operating region, as in FIG. 3, the switch SW is open. 
     FIG. 2A gives a simplified explanation of how parking can be accomplished. When the switch SW is open (as when the ARM resides in the operating region), as shown on the right of FIG. 2A, the switch SW causes a RELAY to deliver battery voltage, B+, to the wiper MOTOR. The MOTOR remains running. 
     When switch SW closes (as when the ARM reaches the parked position), the RELAY in FIG. 2A switches states, and delivers ZERO volts to the MOTOR. The MOTOR stops. The wipers park. 
     Parking System Is Somewhat Redundant 
     Some wiping systems exist which provide intermittent operation of the wipers, for use in light rain. Such systems contain certain components, such as relays, which are also contained in the parking system. 
     These components are redundant, because the intermittent system and the parking system are never used simultaneously. For example, the relays in the parking system and in the intermittent system never operate together. 
     The Inventor has developed an approach to reducing, or eliminating, this redundancy, to reduce cost. 
     OBJECTS OF THE INVENTION 
     An object of the invention is to provide an improved controller for a windshield wiper. 
     A further object of the invention is to provide an intermittent wiper system, which utilizes functionality of a parking system, in order to conserve parts. 
     SUMMARY OF THE INVENTION 
     In one form of the invention, to attain intermittent wiping action, a wiper is first allowed to park. Then, after a time delay, the wiper is withdrawn from the parked position, and allowed to park again. Repetition of this process (park, delay, withdrawal . . . park, delay, withdrawal) produces intermittent wiping. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B schematically illustrate a crank C which drives a wiper ARM. 
     FIG. 2 illustrates a limit switch SW which detects parking of a wiper. 
     FIG. 2A illustrates part of a parking system. 
     FIG. 3 illustrates how the limit switch SW of FIG. 2 opens when the ARM lies within its operating region, outside the parked location. 
     FIG. 4A illustrates logic which the invention implements. 
     FIGS. 4-7 illustrate a circuit which implements one form of the invention. Each Figure emphasizes different parts of the circuit, to explain different stages of operation. 
     FIG. 8 is a more detailed form of the circuit of FIGS.  4 - 7 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Overview 
     Windshield wiping systems generally include parking systems for the wipers. When the driver of a vehicle turns the wiper switch OFF, the parking system takes over. The parking system causes the wiper motor to continue to run, but also senses whether the wipers have reached parked position. When they do, the parking system terminates power to the motor, leaving the wipers in the parked position. 
     One form of the invention may be viewed as adding another function to the parking function. In the added function, after the wipers park, they are allowed to remain parked temporarily. Then, the wipers are withdrawn from the parked position (by actuating the motor). Next, control is returned to the parking system, which parks them again. 
     Thus, the following sequence is executed: 
     park, delay, withdraw; 
     park, delay, withdraw; and so on. 
     This sequence produces intermittent wiping. FIG. 4A is a block diagram which illustrates logic which implements this sequence. In this Figure, the variable N, located at the top, is either fixed, or is a variable under the control of the vehicle driver. 
     Also, the PARKING SYSTEM is entered in two ways: (1) from the block START MOTOR (during intermittent wiping) and (2) from the block START (during shut-down of the wipers). 
     Numerous different types of hardware can be designed which execute this logic. For example, a microprocessor, together with proper sensors (to detect parking) can be programmed to execute the logic. The following discussion will explain one type of hardware developed by the Inventor. 
     One Embodiment 
     Normal Running Mode 
     FIG. 4 illustrates one form of the invention, and illustrates normal running mode. Battery voltage, B+, is applied to terminal T 3 , as indicated, by a switch (not shown) under control of the driver. This voltage causes Darlington pair Q 1  to turn ON, thereby passing current I 1 . This current actuates relay K 1 , causing it to connect terminals T 6  and T 7  together, as indicated by the position of the reed R. Consequently, battery voltage, B+, is applied to terminal T 7 , causing the motor to run continuously. 
     Other components in FIG. 4 drawn in phantom, to indicate that they are not active at this time. 
     Intermittent Mode 
     In FIG. 5, battery voltage B+ is applied to both terminals T 3  and T 5 . Several events now occur. First, Q 1  turns ON, causing relay K 1  to deliver current to the motor, as indicated. 
     At the same time, Darlington pair Q 2  also turns on, delivering current I 2 , which charges capacitor C 2 , as indicated. C 2  becomes fully charged almost instantaneously, because the resistances in the path of I 2  (i.e., the collector-emitter resistance within Q 2  and the resistance of diode CR 1 ) are very small. When C 2  becomes fully charged, transistor Q 3  turns ON. 
     FIG. 6 shows that, when Q 3  turns ON (which is allowed by the battery voltage B+ connected to the collector of Q 3 , via terminal T 3 ), it passes current I 3 . The collector-emitter voltage of Q 3  becomes very low, thereby pulling the base voltage of Darlington Q 1  very low, thereby turning Q 1  OFF, as indicated by the phantom drawing of Q 1  in FIG.  6 . 
     When Q 1  goes OFF, relay K 1  switches into the state shown in FIG. 6, wherein reed R connects terminals T 7  and T 8  together. 
     Terminal T 8  is shown in FIG.  2 A. As explained above, this terminal receives one of two voltages: (1) battery voltage, B+, whenever the wiper ARM resides outside the parked position, or (2) ZERO volts when the ARM becomes parked. 
     When transistor Q 3  switches ON, switching Q 1  OFF, the ARM is moving, and not parked. (At this time, T 8  is connected to B+, as shown in FIG. 2A, and delivers power to the motor.) The wiper motor continues to run until the wiper ARMS (see FIGS. 1 and 2) reach the parked position (shown on the left of FIG.  2 A). When they do, the PARKING CIRCUIT terminates current to the motor, by applying ZERO volts to terminal T 8 , as schematically indicated on the left of FIG.  2 A. 
     With ZERO volts applied to T 8 , Darlington Q 2  now turns OFF, as indicated by the phantom representation in FIG.  7 . With Q 2  OFF, no current is supplied to capacitor C 2 , which now discharges, primarily through resistors R 6  and R 7 , as indicated. When C 2  discharges sufficiently, transistor Q 3  turns OFF, as indicated by the phantom representation, thereby releasing the base of Darlington Q 1 , thereby allowing Q 1  to turn ON, as indicated by the solid, heavy drawing. Now, Q 1  again passes current I 1 , which actuates relay K 1 , which now connects terminals T 6  and T 7  together, as indicated by reed R. (The turning OFF of Q 3  can be termed a RESUME  30  signal, because it causes the motor to resume running, after having been parked.) 
     Terminal T 6  delivers battery voltage, B+, to the motor. The motor now withdraws the now parked ARMS from the parked position. The PARKING CIRCUIT detects this withdrawal, and applies B+ to terminal T 8  (this application of B+ is not shown in FIG.  7 ). 
     The situation now is the same as in FIG.  4 . The sequence described above, running through the sequence of FIGS. 4 through 7, repeats. 
     One View of Invention 
     The preceding events can be grouped as follows. 
     1. Start wiper motor. (Q 1  in FIG. 5 turns ON). 
     2. Give control to the parking system. (K 1  connects T 8  with T 7  in FIG.  6 ). 
     3. Park the ARM. (PARKING CIRCUIT in FIG. 7 senses parking and applies ZERO volts to T 8 ). 
     4. Wait for an interval. (C 2  discharges in FIG.  7 ). 
     5. Withdraw ARM from parked position, by starting motor. (After C 2  discharges, Q 1  turns ON in FIG. 7, causing K 1  to connect T 6  with T 7 .) 
     6. Go to step  2 , and repeat steps 2 through 6. 
     Condensed Sequence 
     This sequence of events can be condensed (conceptually) to the following: 
     1. Withdraw the wipers from parked position. 
     2. Invoke parking function, and park the wipers. 
     3. Allow the wipers to remain parked temporarily. 
     4. Go to step 1. 
     Significant Features 
     1. FIG. 8 is a more detailed schematic of FIGS. 4-7, and provides additional information, such as component values and standardized part numbers (e.g., Darlington Q 1  can take the form of part number 2N7052). 
     In FIG. 8, the diode D, shorting the ends of the coil in relay K 1 , serves to absorb voltage spikes which otherwise occur when current through the coil attempts to terminate. 
     Capacitor Cl serves to prevent relay chatter, because Q 3  turns off slowly. 
     An OPTIONAL JUMPER can be added, which hard-wires terminals T 3  and T 5  together, thereby causing intermittent wiping action to occur at all times (except when washing, discussed below, is requested). 
     2. The duration of the temporary parking of step 3 in the “Condensed Sequence,” above, is determined by the discharge time of C 2 . This discharge time is determined by the RC time constant of the discharge circuit. The resistances of this time constant are dominated by R 6  and R 7 , in FIG. 8, as stated above. These resistances can be made variable, in order to allow the driver to control the duration of the park cycle, by varying these resistances. 
     3. A wash cycle can be invoked by applying B+ temporarily to terminal T 2  in FIG.  7 . This action charges capacitor C 3  very rapidly, which turns ON Darlington Q 4 . Darlington Q 4  actuates relay K 1 , connecting terminal T 6  with T 7 , thereby delivering current to the motor. 
     Current is delivered to the motor until the voltage on C 3  drops below the turn-on voltage of Q 4 . Preferably, the RC discharge time constant of C 3  is set so that the motor runs for about three wiping strokes. 
     Of course, if a continuous voltage is applied to terminal T 2 , the motor runs continuously. Then, after the voltage to T 2  is terminated, the motor continues to run until C 3  discharges sufficiently. 
     A windshield washer pump, not shown, which sprays solvent on the windshield, is actuated directly by the voltage applied to T 2 . That is, when voltage is applied to T 2 , both the pump and the wiper motor operate. When the voltage is removed, the pump stops, but the motor continues until C 3  discharges. 
     4. A preferred use of the invention is in a single-arm wiper used on the rear window of a van. 
     5. One view of the invention is that it alternates between two conditions: 
     A. Running the motor from power obtained from the parking system, as indicated by the power delivered from terminal T 8  in FIG.  6 . 
     B. Running the motor from power obtained from outside the parking system, as indicated by the power delivered from terminal T 6  in FIG.  7 . 
     6. The invention accomplishes intermittent wiping, parking or a wash cycle by the addition of a single relay, namely K 1  in FIGS. 4-8. Viewed another way, the parking system relay serves multi-duty: it operates in the parking system, and it operates in the intermittent system and wash cycle. 
     Numerous substitutions and modifications can be undertaken without departing from the true spirit and scope of the invention. What is desired to be secured by Letters Patent is the invention as defined in the following claims.