GB2313452A

GB2313452A - Windscreen wiper motor controller

Info

Publication number: GB2313452A
Application number: GB9611048A
Authority: GB
Inventors: Benham Javad Ahmadi
Original assignee: ACDTRIDON EUROP Ltd
Current assignee: ACDTRIDON EUROP Ltd
Priority date: 1996-05-25
Filing date: 1996-05-25
Publication date: 1997-11-26
Also published as: GB9611048D0

Abstract

A controller for an windscreen wiper electric motor M with motor supply brushes 1, 2, comprises a control line 16,17 connectable to a first supply voltage VB via a switch S2, a change-over switching device R1 for selectively effecting connection of the motor supply brush 1,2 to a second supply voltage VB or to ground in order selectively to energise the motor M in rotation or to brake the motor M against rotation, and a control device G including control tracks 12,14 rotatable in synchronism with the motor M. The changeover switching device R1 has a control input terminal 15 connected to the control device G and the control line 16,17; the control device G being ineffective during connection of the control line 16,17 to the first supply voltage VB via the switch S2 but, upon opening of the switch S2, being effective to prevent change-over of the switching device R1 whereby the motor M is maintained energised until the control device G reaches a predetermined rotational position at which it initiates change-over of the switching device R1.

Description

CONTROLLER FOR AN ELECTRIC MOTOR DESCRIPTION The present invention relates to a controller for an electric motor and is particularly, though not exclusively, concerned with a controller '.for a windscreen wiper motor for a vehicle.

It is a common problem with windscreen wiper systems that as soon as the vehicle ignition or auxiliary circuits are de-energised, for example, by switching off the ignition switch, the windscreen wipers, if they had been in operation immediately prior to such de-energisation, immediately cease their traverse across the windscreen and come to rest at some position which may well be intermediate the normal traverse end points. This is an inconvenience in known systems.

Nowadays, many windscreen wiper systems provide parking mechanisms which function automatically to park the windscreen wiper arms at a predetermined position at switch-off. Such windscreen wiper systems may suffer from the disadvantage of passing high motor currents through their parking mechanisms in certain circumstances, for example, when there is an accumulation of snow on the plenum parking area designated for parking of the windscreen wiper arms.

Also, in some systems there may be an absence of a positive drive of the wipers to their park position, there being reliance on wiper dynamics to accomplish such movement, with consequent wiper juddering and very high motor currents which result in burning and scorching of components of the windscreen wiper electrical system as well as straining of the motor.

The present invention aims to overcome, or at least substantially reduce, the foregoing disadvantages of known windscreen wiper systems; the present invention particularly provides a controller for an electric motor for a vehicle windscreen wiper system which affords more reliable braking, selfparking upon ignition de-energisation, and functionality which simulates the operation of a mechanical snow clutch; and which is generally more reliable in operation than systems known hitherto.

According to a first aspect, the present invention provides a controller for an electric motor having a motor supply brush, the controller comprising a control line connectable to a first supply voltage via a switch, a change-over switching device for selectively effecting connection of the motor supply brush to a second supply voltage or to ground in order selectively to energise the motor in rotation or to brake the motor against rotation, and a control device including control tracks rotatable in synchronism with the motor, the change-over switching device having a control input terminal connected to the control device and the control line; the control device being ineffective during connection of the control line to the first supply voltage via the switch but, upon opening of the switch, being effective to prevent change-over of the switching device, whereby the motor is maintained energised until the control device reaches a predetermined rotational position at which it initiates change-over of the switching device.

Preferably, the controller of the present invention is adapted for use with a two-speed motor including a first supply brush and a second supply brush, and a further change-over switching device is provided for selectively directing connection of the second supply voltage to the first supply brush for energising the motor at one speed or to the second supply brush for energising the motor at another speed.

Preferably, the or each change-over switching device is constituted by a respective electromechanical relay.

Preferably also, the controller of the present invention comprises a motor supply circuit and a motor control circuit, these circuits being electrically isolated from each other, whereby the control device is not subjected to the flow of motor currents during operation.

According to a second aspect of the present invention, there is provided a device for the control and supply of an electric motor having a motor supply brush, the device comprising a motor supply circuit including a change-over switching device for selectively switching connection of the motor supply brush to a motor supply voltage to energise the motor or to ground to brake the motor; the device also comprising a motor controller including a motor control device rotatable in synchronism with the motor and a motor control circuit having a control line connected to a control input of the change-over switching device, whereby the switch state of the change-over switching device may be selected by the motor controller, and the motor controller being electrically isolated from the motor supply circuit.

Preferably, the device for the control and supply of an electric motor according to the second aspect of the present invention is adapted for use with a two speed motor having a first supply brush and a second supply brush, the device further comprising another change-over switching device for selectively switching connection of the motor supply voltage to one of the first and second supply brushes for energisation of the motor at a first speed or to the other of the first and second supply brushes for energisation of the motor at a second, different speed.

Preferably also, the or each change-over switching device is constituted by an electromechanical relay.

The controller for an electric motor, according to the first aspect of the present invention, or the device for the control and supply of an electric motor, according to the second aspect of the present invention, may be adapted for use with a vehicle electric windscreen wiper system in which the electric motor is arranged to drive one or more windscreen wiper arms to traverse across a vehicle windscreen in forward and reverse motions.

In a device according to either aspect of the present invention, the control device includes one or more electrically conductive tracks and electrically non-conductive regions and associated contact fingers, the arrangement of the track(s) and fingers being such as to determine a windscreen wiper arm parked position of the motor at which the motor will also be electrically braked and locked.

In embodiments of the present invention, the control line is connected to a windscreen wiper on/off switch capable of being connected to a vehicle electrical supply, for example as provided by the vehicle battery, via the vehicle ignition/auxiliary circuit switch.

In a vehicle windscreen wiper system incorporating a device according to either aspect of the present invention, opening of either of the windscreen wiper on/off or vehicle ignition/auxiliary circuit switches whilst the windscreen wipers are in operation, does not lead to immediate cessation of the normal traverse of the windscreen wiper arm(s) across the vehicle windscreen, but instead ensures continuance of such traverse until a windscreen wiper arm parking position is reached, at which point the motor supply brush is grounded due to de-energisation of the first-mentioned change-over switching device or electro-mechanical relay. If the windscreen wipers had been operating in high speed mode prior to opening of either of the aforementioned switches, automatic switching to low speed mode is ensured prior to the parking of the windscreen wiper arms(s).

In some realisations according to either aspect of the present invention, the controlled parking and braking is effected solely under the control functions exercised by the control device with its electrically conductive tracks, whilst in other realisations the control device with its electrically conductive tracks may be associated with an electrical or electronic 6et/reset latch offering further improved functionality. The provision of the set/reset latch enables a mechanical snow clutch to be omitted from the windscreen wiper system The invention extends to a vehicle windscreen wiper system embodying the controller for, or the device for the control and supply of, an electric motor according to the first or second aspect of the invention.

The present invention, in a third aspect, provides a method of operating a vehicle windscreen wiper system comprising an electric motor arranged to operate one or more windscreen wiper arms, the motor having a supply brush; the system further comprising a first change-over switching device for selectively switching connection of the motor supply brush to a motor supply voltage to energise the motor or to ground to brake the motor, a control device rotatable in synchronism with the motor and connected via a control line to a control input of the first changeover switching device whereby the switch state of the first change-over switching device may be selected by the control device; wherein change-over of the first change-over switching device to its state at which it is effective to connect the motor supply brush to ground to brake the motor is delayed, relative to the time of disconnecting a first supply voltage source from the control input, by the operation of the control device.

The present invention will now be described in greater detail, and by way only of example, with reference to the accompanying illustrative drawings in which: Figure 1 is a diagrammatic illustration of part of a windscreen wiper system for a vehicle, embodying a controller according to the present invention; Figure 2 is a diagrammatic illustration similar to that of Figure 1, but showing a modified motor circuit; and Figure 3 is a diagrammatic illustration similar to that of Figure 1 but showing a modified motor control circuit.

Referring to Figure 1 of the drawings, there is shown an electric motor M for operating windscreen wipers of a vehicle, the motor M having a first commutator brush 1, a second commutator brush 2, and a common brush 3 connected by line 24 to ground.

Mounted so as to be rotated by or with the armature of the motor M is a gear wheel in the windscreen wiper arm drive chain and affording a control disc, generally indicated at G, of electrically insulating material. One of the circular faces of the control disc G is provided with an electrically conductive track 12, part of whose outer periphery is interrupted so as to provide an electrically non-conductive segment 14. The track 12 is connected directly, by way of a contact finger 13, to a voltage source VB, constituted by the vehicle battery. A second contact finger 15 is provided and disposed to contact either the electrically nonconductive segment 14 or the electrically conductive portion of the track 12, according to the rotational position of the control disc G.

The windscreen wiper system operates through a main on/off switch S1 constituted by the vehicle ignition/auxiliary switch which is supplied directly from the voltage source vB. Switch S1 is connected in series with the windscreen wiper on/off switch S2, and there is a third switch S3 for switching the wipers between low and high speeds. This latter switch S3 is associated with a motor low/high speed relay R2.

The control disc G is associated with a relay R1 for the controlled braking and parking of the windscreen wiper arms, as will be described below.

The mode of operation of the controller of the present invention will now be described, commencing with the configuration as shown in Figure 1.

With the circuit in the configuration shown in Figure 1, the windscreen wiper system is inoperative, with the windscreen wiper arms in their parked positions, and the vehicle ignition off. During vehicle operation, with the vehicle ignition circuits energised, the switch S1 will be closed and if it is required to operate the vehicle windscreen wipers all that is then necessary is to close the switch S2, whereby the switch wiper moves across from the switch open terminal 8 to the switch closed terminal 9.

Assuming that the windscreen wipers are required to operate in low speed mode, the third switch S3 will remain in the position shown. With the switches S1, S2 and S3 in the positions just described, voltage from the voltage source VB passes along lines 18, 17 and through the energisation coil of relay R1 in order to cause this relay to flip its operating state.

Thus, the contact arm of this relay moves from the normally closed contact 10 to the normally open contact 11 and, in so doing, completes a circuit from the voltage source VB through the line 26 and normally closed contact 5 of the relay R2 to line 25 which supplies the second commutator brush 2 of the motor M.

The motor thus commences rotation in its low speed mode, simultaneously driving the control disc G so that the fingers 13, 15 move relative to the track segments 12, 14 thereof. So long as the vehicle ignition/auxiliary circuit switch S1 and windscreen wiper on/off switch S2 remain in the positions described, the windscreen wipers continue their normal operation unaffected by the control disc G. Should the windscreen wipers be required to operate in high speed mode, the speed control switch S3 is switched over so that its wiper moves across from the low speed terminal 6 to the high speed terminal 7. Voltage from the voltage source VB then passes through the energisation coil of the relay R2 in order to cause this to flip, whereby its contact arm moves from its normally closed terminal 5 to its normally open terminal 4. Motor current then passes through the supply commutator brush 1 in order to operate the motor at high speed. The motor circuit is shown drawn in extra heavy lines, and it is to this circuit that the very high motor currents are restricted.

Throughout the rest of the circuit of the windscreen wiper system, shown in lighter lines, it is only low currents which circulate.

If, during operation of the windscreen wipers in either low or high speed mode, either one or both of the switches S1, S2 are opened, thus disconnecting the main supply line 20 and its associated voltage source VB from the windscreen wiper system, the following operation will occur.

Assuming that the windscreen wiper arms are at some point in their traverse across the windscreen and intermediate the normal end points of their traverse, both contact fingers 13, 15 of the control disc G will be on the conductive track 12. This being the case, continuity of the circuit from the supply voltage VB to the relay R1 is ensured through the line from the voltage source VB to the contact finger 13 and thence via the track 12, contact finger 15, and lines 16, 17.

Thus the windscreen wiper motor M continues its function uninterrupted. Eventually, however, the rotational position of the control disc G is such that, whilst the contact finger 13 remains on the conductive track 12, the contact finger 15 passes on to the non-conductive segment 14. This causes interruption of the voltage supply from the source VB, with the result that the energisation coil of the relay R1 is no longer supplied and the relay flips state so that its contact arm moves off its normally open terminal 11 to its normally closed terminal 10.

Supply voltage from the voltage source VB to the motor M is, thus, interrupted and the commutator supply brush and the common brush 3 are grounded via the lines 23, 24.

Thus, it will be seen that the vehicle windscreen wiper arms have continued to move until they reach their parked position and, having reached that position, they are now effectively electrically braked and locked in this position by the grounding of the supply and common motor brushes. It will be understood that because the circuit is wired up such that all power inputs come directly from the vehicle battery and not from the ignition circuit, only low control currents pass through the windscreen wiper arm control circuit, with concurrent avoidance of high currents being switched mechanically, which obviates sparking and arcing.

Compared with a known arrangement using a similar control disc, in the present invention the arcuate extent of the segment 14 extends over the arc B-C, relative to the rather larger extent of the arc A-D used in a known system. This gives a more positive braking effect and, by reducing the park angle, eliminates any tendency of the windscreen wiper arms to freewheel, which was the case in the known system.

Furthermore, in the present invention an additional segment of the control disc, shown at the inner periphery and in dotted lines and associated with a further control finger and line passing to ground (also shown in dotted lines), are obviated.

If, at the instant of opening the switches Sl,S2, the windscreen wipers are operating in their high speed mode, the first operation, effected prior to the braking and parking sequence described above, is automatically to switch the motor to its low speed mode. This is accomplished as follows.

Inclusion of a diode D, as shown in Figure 1, in the line 18 ensures that when either switch S1,S2 is opened voltage may not pass from the source VB via the control disc G, lines 16, 18 and 19, and switch S3 to the energisation coil of the speed control relay R2.

Thus deprived of its supply voltage, relay R2 flips state whereby its contact arm moves off the normally open terminal 4 to the normally closed terminal 5.

Motor current then passes to the commutator supply brush 2 in order to operate the motor at low speed.

This automatic switching down to low speed mode takes place regardless of the rotational position of the control disc G; and, because the wipers are reverted to their low speed mode prior to braking and parking, the chances of them overshooting the park position are reduced.

Turning now to Figure 2, it will be seen that the control circuit is identical to that of Figure 1, but the motor supply circuit is modified to accommodate a motor M of reverse polarity which is inversely powered up. Thus, it will be seen that the normally open terminal 11 of the relay R1 is here grounded, whilst the common commutator brush 3 of the motor M is connected to the voltage source VB. Operation of the windscreen wiper system of this Figure is otherwise the same as that described above in relation to Figure 1. Thus, another advantage of the controller of the present invention is to reduce the number of variations for different applications, because the control circuit remains the same regardless of whether the motor is left or right hand, or inversely magnetised etc.

In the present invention, the fact that the system brakes with the relays R1,R2 in the normally closed positions, means that no quiescent current is drawn from the battery once the relays have flipped and the wipers are in their parked positions.

Figure 3 shows a modification of the controller of the present invention, further improved over the arrangements described above in relation to Figures 1 and 2. In connection with the arrangements of Figures 1 and 2, once the windscreen wipers have been parked and turned off, and in conditions where there is snow packed on the windscreen, in certain systems it is possible for the snow to push the wiper arms back from their normal parked position, thus causing some small rotation of the control disc G to the point where the contact fingers once again make a circuit from the voltage source VB through the conductive track 12.

This re-activates the wipers and could result in battery drain. One way around this problem is to incorporate a mechanical snow clutch which, once the windscreen wiper arms are parked, will prevent any reverse movement of the contact fingers with the wiper arms. The arrangement of Figure 3 is an alternative to the provision of such a mechanical snow clutch.

The arrangement of Figure 3 is similar to that shown in Figure 1, and the same reference numerals are used to denote like parts.

As seen in Figure 3, the control disc G has an electrically conductive track 12 which, in this case, is completely uninterrupted around its periphery so that the former segment 14 of Figure 1 (here shown only in dotted lines) and its associated contact finger 15 of Figure 1 are now absent. Instead, at the inner periphery of the track 12 and extending over the arc B-C, is a conductive segment 14' and associated contact finger 15' and line 16' connected to the reset terminal 18a of a set/reset latch 18'. The latch 18' also has a set terminal 18b.

In operation, when either of the ignition/auxiliary switch S1 and windscreen wiper on/off switch S2 is moved to the off position, the latch 18' holds the energisation line 17 of the relay R1 high, so that the motor M continues to be supplied from the voltage source VB, ensuring continuance of the wiper arm traverse across the windscreen and rotation of the control disc G. Eventually, the contact finger 15' moves off a non-conductive region of the control disc G by crossing either edge B or C on to the conductive segment 14'. At this juncture, the line 16' is connected to the voltage source VB and the reset terminal 18a of the latch 18' goes high, leading to de-energisation of the relay R1 with consequent parking of the windscreen wiper arms and braking of the motor M by grounding at both its supply and common brushes, as described in relation to Figure 1.

Once the windscreen wiper arms are parked and the latch 18' has been reset, if the windscreen wiper arms move back from their parked position for any reason, for example due to snow pack, the motor M cannot be re-energised until the latch 18' has been set again which occurs only when either the ignition/auxiliary switch S1 or windscreen wiper on/off switch S2 is next closed to send the set terminal 18B of the latch 18' high.

An arrangement similar to that of Figure 3, incorporating the set/reset latch 18', may also be applied to a reverse polarity circuit as shown in Figure 2.

From the foregoing description of the currently preferred embodiments of the present invention, it will be seen that self parking of the windscreen wiper arms occurs upon ignition off, and that improved braking is provided for at all times, especially during the occurrence of snow packing on the windscreen. Further, there is no risk of the windscreen wiper arms freewheeling at any point in their traverse, and because the control circuitry involves only low current, there are no sparks, electrical noise, burnt tracks or fingers, and no damage to the control disc G arising from any such causes. Due to the reduced arcuate extent of the segment 14 or 14', compared with known arrangements, there is tighter control of the windscreen wiper arm parking position. A reduction in the number of tracks and contact fingers on the control disc G enables the use of a reduced wire harness. The embodiment of Figure 3 obviates the provision of a mechanical snow clutch. The number of circuit variations due to the need to accommodate both left and right hand drive, or reverse biased, motors is reduced.

The above noted advantages of the present invention are accompanied by a reduction in manufacturing and operating costs, and an improvement in product reliability.

Whilst the present invention has been described hereinabove in relation to details of the currently preferred embodiments, its scope is in no way intended to be limited by such details, but instead is intended to extend to all such variations as fall within the scope of the present invention as defined in the appended claims.

Claims

1. A controller for an electric motor having a motor supply brush, the controller comprising a control line connectable to a first supply voltage via a switch, a change-over switching device for selectively effecting connection of the motor supply brush to a second supply voltage or to ground in order selectively to energise the motor in rotation or to brake the motor against rotation, and a control device including control tracks rotatable in synchronism with the motor, the change-over switching device having a control input terminal connected to the control device and the control line; the control device being ineffective during connection of the control line to the first supply voltage via the switch but, upon opening of the switch, being effective to prevent change-over of the switching device, whereby the motor is maintained energised until the control device reaches a predetermined rotational position at which it initiates change-over of the switching device.

2. The controller according to claim 1, which is adapted for use with a two-speed motor including a first supply brush and a second supply brush, and wherein a further change-over switching device is provided for selectively directing connection of the second supply voltage to the first supply brush for energising the motor at one speed or to the second supply brush for energising the motor at another speed.

3. The controller according to claim 1 or claim 2, wherein the or each change-over switching device is constituted by a respective electro-mechanical relay.

4. The controller according to any preceding claim, comprising a motor supply circuit and a motor control circuit, these circuits being electrically isolated from each other, whereby the control device is not subjected to the flow of motor currents during operation.

5. A device for the control and supply of an electric motor having a motor supply brush, the device comprising a motor supply circuit including a changeover switching device for selectively switching connection of the motor supply brush to a motor supply voltage to energise the motor or to ground to brake the motor; the device also comprising a motor controller including a motor control device rotatable in synchronism with the motor and a motor control circuit having a control line connected to a control input of the change-over switching device, whereby the switch state of the change-over switching device may be selected by the motor controller, and the motor controller being electrically isolated from the motor supply circuit.

6. The device for the control and supply of an electric motor according to claim 5, which is adapted for use with a two-speed motor having a first supply brush and a second supply brush, the device further comprising a further change-over switching device for selectively switching connection of the motor supply voltage to one of the first and second supply brushes for energisation of the motor at a first speed or to the other of the first and second supply brushes for energisation of the motor at a second, different speed.

7. The device according to claim 5 or claim 6, wherein the or each change-over switching device is constituted by a respective electro-mechanical relay.

8. The controller for an electric motor, according to any one of claims 1 to 4, or the device for the control and supply of an electric motor, according to any one of claims 5 to 7, adapted for use with a vehicle electric windscreen wiper system in which the electric motor is arranged to drive one or more windscreen wiper arms to traverse across a vehicle windscreen in forward and reverse motions.

9. The invention according to any preceding claim, wherein the control device includes one or more electrically conductive tracks and electrically nonconductive regions and associated contact fingers, the arrangement of the track(s) and fingers being such as to determine a parked position of the motor at which the motor will also be electrically braked and locked.

10. The invention according to claim 9, embodied in a vehicle windscreen wiper system and wherein the parked position of the motor corresponds with a parked position of one or more windscreen wiper arms.

11. The invention according to claim 10, wherein the control line is connected to a windscreen wiper on/off switch capable of being connected to a vehicle electrical supply via a vehicle ignition/auxiliary circuit switch.

12. The invention according to claim 2, or any claim appended thereto, or according to claim 6, or any claim appended thereto, wherein means are provided in the control line to ensure that the further changeover switching device is switched to its state in which it switches connection of the motor supply voltage to whichever of the first and second supply brushes corresponds to energisation of the motor at the lower of the two speeds as soon as the or a first supply voltage to the first-mentioned change-over switching device is interrupted.

13. The invention according to claim 12, wherein the means comprises a diode.

14. The invention according to any of claims 1 to 12, wherein the means comprises a set/reset latch.

15. The invention according to claim 14, wherein the latch has a reset terminal connected to the control device and a set terminal connected to a switch by which connection and disconnection of the, or a, first supply voltage may be effected.

16. The invention according to claim 15, wherein the latch has an output terminal connected to the firstmentioned change-over switching device; the arrangement being such that, upon connection of the, or a, first supply voltage by closing the switch, the latch is set so as to enable control of the firstmentioned change-over switching device via the latch and, upon disconnection of the, or a, first supply voltage by opening the switch, the latch remains set until its reset terminal receives a voltage from the control device whereupon the latch is reset so as to disable control of the first -mentioned change-over switching device from the control device via the latch.

17. A method of operating a vehicle windscreen wiper system comprising an electric motor arranged to operate one or more windscreen wiper arms, the motor having a supply brush; the system further comprising a first change-over switching device for selectively switching connection of the motor supply brush to a motor supply voltage to energise the motor or to ground to brake the motor, a control device rotatable in synchronism with the motor and connected via a control line to a control input of the first changeover switching device whereby the switch state of the first change-over switching device may be selected by the control device; wherein change-over of the first change-over switching device to its state at which it is effective to connect the motor supply brush to ground to brake the motor is delayed, relative to the time of disconnecting a first supply voltage source from the control input, by the operation of the control device.

18. A method according to claim 17, the system further comprising a second change-over switching device for selectively switching connection of the motor supply voltage between a first low speed motor supply brush and a second high speed motor supply brush; and wherein change-over of the first changeover switching device to its state at which it is effective to connect the motor supply brush to ground to brake the motor is preceded by change-over of the second change-over switching device to its state at which it is effective to connect the motor supply voltage to the first low speed motor supply brush.

19. A vehicle windscreen wiper system comprising an electric motor arranged to operate one or more windscreen wiper arms, the motor having a first low speed supply brush, a second high speed supply brush and a common ground brush, a first change-over switching device for selectively effecting connection of a motor supply terminal either to a motor supply voltage for energising the motor or to ground for braking the motor, a second change-over switching device for selectively effecting connection of either the first or the second supply brush to the motor supply terminal for selecting the motor speed, a first control voltage source, a control line including a main switch connected or connectable between the first control voltage source and a control input of the first change-over switching device, and a control device rotatable in synchronism with the motor, the control device having electrically conductive and nonconductive paths and associated contact fingers, one contact finger being connected or connectable to a second control voltage source and another contact finger being connected or connectable to the control input of the first change-over switching device; the arrangement being such that, in operation and with the main switch closed, voltage from the first control voltage source enables the first change-over switching device to its state in which it effects connection of the motor supply terminal to the motor supply voltage to energise the motor in rotation and the control device is ineffective but, upon opening of the main switch, the control device becomes effective to hold the first change-over switching device in the same said state whilst the control device continues to rotate with the motor until the control device reaches a predetermined position of rotation at which it initiates change-over of the first change-over switching device to its state in which it effects connection of the motor supply terminal to ground to brake the motor, whereby motor braking is dependent solely on the predetermined position of rotation of the control device and such position corresponds with the arrival of the or each windscreen wiper arm at a parking position.

20. A vehicle windscreen wiper system according to claim 19, including an auxiliary switch connected in an auxiliary control line to a control input of the second change-over switching device for selecting the state of the latter, the auxiliary switch being in series with the main switch for selecting low or high speed of the motor when the main switch is closed, and blocking means associated with the auxiliary control line and effective, upon opening of the main switch, to prevent energisation of the control input of the second change-over switching device via the control device whereby at the instant of opening the main switch, the second change-over switching device is switched to, or held at, its state in which low speed of the motor is selected.

21. A vehicle windscreen wiper system according to claim 19 or claim 20, including a set/reset latch having a set terminal connected to the main switch and the auxiliary switch, a reset terminal connected to the control device, and an output terminal connected to the control input of the first change-over switching device whereby, upon opening of the main switch, and after braking of the motor and parking of the windscreen wiper arms, the latch is effective to disable connection between the control device and the control input of the first change-over Switching device until next closure of the main switch to resaet the latch, such disablement being effective, i-n case of physical movement of the windscreen wiper from the parked position and with corresponding rotation of the control device, to prevent connection of the second control voltage source via the control device to the control input of the first change-over switching device, thereby preventing re-energisation of the motor and/or draining of any or all of the supply voltage sources.

22. A controller for an electric motor, substantially as hereinbefore described with reference to Figure 1 or Figure 2, and with or without the modification of Figure 3, of the accompanying drawings.

23. A device for the control and supply of an electric motor, substantially as hereinbefore described with reference to Figure 1 or Figure 2, and with or without the modification of Figure 3, of the accompanying drawings.

24. A vehicle windscreen wiper system, substantially as hereinbefore described with reference to Figure 1 or Figure 2, and with or without the modification of Figure 3, of the accompanying drawings.

25. A method of operating a vehicle windscreen wiper system, substantially as hereinbefore described with reference to Figure 1 or Figure 2, and with or without the modification of Figure 3, of the accompanying drawings.