GB2142226A - Vehicle screen wiper systems - Google Patents

Abstract

A vehicle windscreen wiper system having off screen parking and intermittent wipe provisions in which the wipers are parked on screen during intermittent wipe operation, but the off-screen parking position is reached by motor reversal when "off" is selected. To this end there are provided two limit switches L/S1 and L/S2 one of which corresponds to a first on screen position during forward running of the motor M and to an off screen position during reverse running and the other of which corresponds to a second on screen position. The control circuit includes relays RL1 and RL2 controlling forward and reverse running, reverse running being selected only when the second limit switch L/S2 is actuated whilst "off" is selected. <IMAGE>

Description

SPECIFICATION Vehicle screen wiper systems This invention relates to vehicle screen wiper systems ofthe kind using a reversible motor which is driven forwardly for normal wiping action, but which is driven in reverse when wiping is stopped to cause the wiper blades to bedriven off the screen to a parking position. The mechanism which connects the motortothewiperbladedrive incorporates a known extended crank arrangement (see, e.g. UK-A2013,817) such that when the motor is in reverse the arc swept by the blade is different from that swept during forward drive.

Difficulties arise when an attempt is made to incorporate an intermittentwipe facility in a conventional off-screen parking system as outlined above.

Whilstitisasimplematterto incorporate an intermittent wipe facility with the blade parking off-screen during the dwell periods, this is undesirable since the blade must cross the screen rubber on each stroke and this tends to be a noisy operation.

It is accordingly an object ofthe present invention to provide a system in which both off screen blade parking and an intermittent wipefacility are readily available without requiring major modifications to the mechanical design ofthe blade drive unit.

Broadly, the invention provides a screen wiper system incorporating a reversible blade drive motor unit arranged when driven in reverse to drive the blade to an off-screen parking position; a first limit switch operated by said blade drive motor when the latter is at a first limit position corresponding to a first blade motion reversing position when the motor is driven forwardly and to an off-screen parking position when the motor is driven in reverse; a second limit switch operated by said blade drive motor unit when the latter is at a second limit position corresponding to a second blade motion reversing position; and electrical circuit means whereby said first limit switch controls stopping of the motor during intermittent wipe-operation, but said second limit switch controls reversal of the motor at said second limit position when off-screen parking is selected.

Preferably said electrical circuit means includes first and second relays connecting the motorto a supplyto provide forward running when only said first relay is energised and reverse running when only said second relay is energised. With such an arrangement, when both relays are de-energised, a short-circuit is preferably provided across the motorfor braking.

The accompanying drawing is an electrical circuit diagram showing one example of a screen wiper system in accordance with the invention.

As shown in the drawing the motor 17, which of the wiper motor unit has its fast, and slow brushes F and S connected via one pole 20aof a selector switch 20 to a terminal 2 of a control circuit 21. This terminal 2 is connected to the common contactterminal RL1Aofa changeover relay RL1 controlling forward drive of the motor. The normally closed contact RL1 B of relay RL1 is connected to a grounded terminal 6 of the circuit and the normally open contact RL1C is connected to a terminal 4 of the circuit, which is connected, in use, to the vehicle battery via a contact of the ignition switch (not shown).The other brush of motor M is connected via a terminal 8 of the circuitto the common contact terminal RL2A of a reversing relay RL2, which has its normally closed contact RL2B and its normally open contact RL2C connected respectively to terminals 6 and 4.

The motor unit includes two limitswitches L/S1 and US2. The first limit switch US1 is closed except when the motor unit is in a first limit position corresponding to a first blade direction reversing position when the motor is being driven in forward direction, but to an off-screen blade parking position when the motor has been driven in reverse direction as a result ofthe known extended crank arrangement incorporated in the motor unit. Limit switch US2 is closed except when the motor unit is in a second limit position corresponding to a second blade direction reversing position (i.e. at the end of the blade sweep opposite the end atwhich parking is effected). Switches LIS1 and US2 respectively connect terminal 2 to terminals 9 and 3 of the circuit.

The winding of relay RL1 is connected at one end to a terminal 1 of the circuit, which terminal is connected to the ignition switch controlled supply by a portion 20boftheselectorswitch 20 when fast or slow running have been selected or by a flick-wipe switch 20C incorporated in the selector switch 20. The other end of relay winding RL1 is connected to the ground terminal 6.Thefirst-mentioned end of relaywinding RL1 is also connected to the collector of a pnp transistor, T1 the emitter of which is connected via a diode D2to the terminal 3, that relay RL1 can be latched in its energised condition when switch LJS2 is closed and transistorT1 is conductive.

The first-mentioned end of the relay winding RL1 is also connected to the collector of another pnp transistorT3 which has its emitter connected to the cathode of a diode D1 the anode of which is connected to terminal 4.TransistorT3 is controlled by an intermittent wipe timer as will be explained hereinafter.

Terminal 9 of the circuit is connected to one end of the relaywinding RL2 which has its other end connected to the collector of a pnp transistorT7 the emitter of which is connected to the cathode of the diode D1. The said one end of relay winding RL2 is also connected to the anode of a diode D6 which has its cathode connected to the collector of an npn transistor T2, the emitter of which is connected to said one end of the relaywinding RL1.

TransistorT1 has its base connected by a resistor RX to the anode of a diode Da the cathode of which is connected by a resistor R16 fo the ground terminal 6.

The anode of diode D5 is also connected by a resistor RZ to the base ofthetransistorT7. Aterminal 7 ofthe circuit, which is connected by switch 20bto the supply when intermittent wipe is selected, is connected to the anode of a diode D7the cathode of which is connected The drawing(s) originally filed was (were) informal and the print here reproduced is taken from a later filed formal copy.

to the cathode ofthe diode D5. Terminal 7 is also connected to the anode of a diode D9 the cathode of which is connected to the anode of a diode D8, the cathode of which is connected by a resistor R13 to the base ofthetransistorT2.

The intermittent wipe timer referred to above, incorporates an integrated circuit 21 which produces at an output pin 21 aa train of negative going output pulses spaced bya delay determined byan external variable resistor22 and an external capacitor C1. The i.c. 21 has an input pin 21 band is such thatthe output atthe pin 21 airs held lowwheneverthe input at terminal 21 bis high.Asupplyterminal 21 Cis connected by a resistor R1 2 to the cathode of the diode D.

The variable resistor 22 is connected atone end to the ignition switch controlled supply and at the other end via a terminal 11, to the collector of an npn transistorT4,the emitter of which is connected by a resistor R#to an inputterminal 21 dof i.c. 21. The base ofthe transistorT4 is connected by a resistor R4 to the cathode ofthe diode Dug, so that the transistorT4 is conductive and the timer i.c. therefore runs, when the switch 20bis in the intermittent wipe position.The output ofthe timer i.c. 21 is shunted by an npn transistor Te the emitter of which is connected to the ground terminal 6. Another npn transistor Tg shunts the base of transistor Tg fo the ground terminal 6.The base oftransistorT6 is also connected bya resistor R7 to the cathode of a diode D3, the anode of which is connected to the cathode of diode Dg. A capacitor C3 connects the cathode of the diode D3totheground terminal 6 and a resistor Re connects the base of transistorT5 to the cathode of diode Dug. the circuit elements associated with transistorT5 and Te operate as a one-shot pulse generatorwhich is primed when the intermittent mode is selected (i.e. capacitor C3 charges up but transistor Te is held off because transistorT5 is conductive), and fired when the selector switch 20 is moved out ofthe intermittent position.

The outputterminal ofthe i.c. 21 and the collector of transistorT6 are connected via a resistor R3 to the base of transistorT3, a further resistor B14 connecting the base oftransistor T3 to its emitter.

Terminal 9 of the circuit is connected by a resistor Rg to a terminal 21 eof i.c. 21 to provide a further input to the i.c. 21 so as to inhibit production of a pulse by the i.c. 21 unlesstheswitch US1 is open.

In use, for normal fast or slow running, the switch 20 is put into the appropriate position and the relay RL1 is directly energised via terminal 1 and switch 20b. When switch 20 is returned to the off position, transistorT1 is turned on via resistor R, diode D5 and Era6. Relay RL1 is thus latched through the limit switch US2. When switch US2 opens relay RL1 drops out, thereby providing a path to earth for relay RL2 via USI and RUB. Relay RL2 is thus energised since transistorT7 is biased to conduct via resistor R2, diode D6 and resistor Tri 6. The motor thus reverses driving the blade to its off-screen parking position, atwhich switch US1 opens and breaks the relay RL2 energisation circuit.

When switch 20 is placed in the intermittent position, transistorT7 is biased off so that no current can flow in relay winding RL2, whatever the condition of the other switches. TransistorT4turns on and a pulse is immediately produced by i.c. 21 ,turning on transistor T3 and thereby energising relay winding RL1. Switch US1 nowprovideslatchingactionforthe relay RL1, via D6 and T2 which is held on bythe high signal atterminal 7. Relay RL1 thus drops out when switch US 1 reopens, i.e. with the blade at the on-screen park position. After the set delay another pulse is produced by i.c. 21 energising relay RL1 again and this cycle continues until switch 20 is moved to the off position.TransistorT6 is then rendered conductive for as long as it takes for capacitor C3 to discharge through the transistorT6 base-emitter. Thus, irrespective ofwhetherthe motorwas running or dwelling at the instant ofswitch-offthe motor will run forwardly until Returns off, continue running forwardly until the next break of switch LS2 and then run in reverse as above mentioned until the off-screen parking position is reached.

The pin 21 bof the i.c. 21 mentioned above is connected by a diode D4 and a resistor R8 to a terminal 10 which is controlled by a screen wash switch 20d A capacitor C2 connects pin 21 bto ground terminal 6.

The forward relay RL1 is energised when the switch 2Odis closed and remains energised until the capacitor C2 discharges following release of switch 20d The normal off-screen parking sequence then follows.

Claims (5)

1. Avehicle screen wiper system incorporating a reversible blade drive motor unit arranged when driven in reverse to drive the blade to an off-screen parking position; a first limit switch operated by said blade drive motorwhen the latter is ata first limit position corresponding to a first blade motion reversing position when the motor is driven forwardly and to an off-screen parking position when the motor is driven in reverse; a second limit switch operated by said blade drive motor unit when the latter is ata second limit position corresponding to a second blade motion reversing position; and electrical circuit means whereby said first limit switch controls stopping of the motor during intermittent wipe-operation, but said second limit switch controls reversal ofthe motor at said second limit position when off-screen parking is selected.

2. A system as claimed in claim 1 in which said electrical circuit means includes first and second relays connecting the motorto a supplyto provide forward running when only said first relay is energised and reverse running when only said second relay is energised.

3. A system as claimed in claim 2 in which the relays are connected so that when both are deenergised the motor is short-circuited.

4. A system as claimed in claim 2 in which both limit switches are connected at one side to a contact of said first relay which grounds them or connects them to the supply according to the state of said first relay.

5. A vehicle windscreen wiper system substantially as hereinbefore described with reference to the accompanying drawings.