GB2309802A - Two-speed motor control system - Google Patents

Abstract

A two speed motor M eg for a windscreen wiper has a high speed brush 2 and a low speed brush 1 and a sequence control device 8 comprising a control track driven in synchronism with the motor. When high speed operation is selected S1, the control track operates to cause the motor to be driven alternately at high and low speed at desired intervals in the rotation of the motor. The aim is to reduce the speed of the motor when the wiper approaches the extremes of its motion.

Description

CONTROLLER FOR A TWO-SPEED MOTOR The present invention relates to a controller for a two-speed motor and is particularly, but not exclusively, concerned with such a controller for use with a windscreen wiper motor for a vehicle.

It is well known in the art to provide for the switching of windscreen wiper motors between low and high speed settings, such switching effecting a change of electrical supply between two supply brushes of the motors, namely a low speed supply brush and a high speed supply brush.

In operation of the windscreen wipers, they execute forward and reverse sweeps, as is well known, whether the motor is operated in its normal low speed mode or the high speed mode. In the low speed mode, there is normally no problem as the wipers approach their sweep extremities and corresponding direction reversal points but in the high speed mode, it is desirable to slow the movement of the wipers on approaching its sweep extremities and direction reversal points. As soon as a reversal point has been traversed, it is then necessary to switch the motor back to its high speed mode for the next wiper sweep, again reducing the speed at the subsequent sweep extremity and directional reversal point. In the prior art, resort is made to costly microprocessors and/or logic circuits to achieve this automatic switching in high speed mode.

It is an object of the present invention to provide a controller for a two-speed motor in which, during operation in its high speed mode, automatic switching may be achieved by an effective, yet more economic arrangement than has hitherto been available.

Accordingly, the present invention provides a controller for a two-speed motor having a first supply brush and a second supply brush, the controller comprising a switching device for selectively directing connection from a supply voltage to a desired one of the first and second supply brushes in order to selectively energise the motor at either a low speed or a high speed, and a sequence control device comprising a control track rotatable in synchronism with the motor and arranged to sequence the motor from its high speed to its low speed and back to its high speed at desired intervals in the rotation of the motor, the sequence control device being rendered operative upon operation of the switching device to select high speed energisation of the motor.

Preferably, the switching device includes an electro-mechanical relay having its normally-closed contact connected to the first supply brush of the motor. This first supply brush may be the low speed motor supply brush. The switching device may further include a switch which1 when closed, causes energisation of this relay so that its associated input signal line is switched to a normally-open contact which is connected to the second motor supply brush. This second supply brush may be the high speed motor supply brush.

The control track of the sequence control device may be connected electrically in series with an energisation line of the switching device, in order to de-energise and re-energise automatically the relay of the switching device, to provide the specified sequencing of the motor speed.

Preferably, the sequence control device comprises an electrically non-conductive disc which is rotatable by or with the motor and on which the control track is provided, the control track preferably comprising alternating electrically conductive and electrically non-conductive sectors therearound which form a closed geometric figure, such as an annulus.

The control track may be arranged such that it provides two electrically conductive sectors alternating therearound with two electrically nonconductive sectors.

If the controller of the present invention is adapted to control a two speed motor for a vehicle windscreen wiper, then each electrically conductive sector can correspond to a normal sweep of the windscreen wiper across the windscreen, whilst each electrically non-conductive sector can correspond to a region of the windscreen wiper sweep adjacent its extremity and direction reversal point.

The inventive controller may also comprise a second switching device which can include an electromechanical relay having a normally-open contact connected to ground. This second switching device may further include an on/off switch. When the on/off switch is open, the relay can be de-energised and connection made from a supply voltage, such as a vehicle's 12 volt supply line, through the normallyclosed contact of the relay to its associated output signal line which conducts the supply voltage to the input signal line of the relay of the first-mentioned switching device. When, on the other hand, the on/off switch of the second switching device is closed, it causes energisation of its associated relay to switch its output signal line to its normally-open contact connected to ground. This causes the motor to be dynamically braked to a stop.

Preferably, the sequence control device further comprises a brake track which, when the on/off switch of the second switching device is closed with consequential energisation of its associated relay, causes one or other of the first and second motor supply brushes to be connected directly to ground in order to provide for the aforesaid dynamic braking of the motor and, hence, any associated windscreen wiper.

The controller for a two speed motor according to the present invention thus enables a vehicle windscreen wiper to be operated in either a normal low speed mode or in a high speed mode during which latter mode the motor is automatically slowed as its approaches its direction reversal point and then, once again, is returned to its high speed mode for the following sweep of the wiper across the windscreen.

At its approach to the opposite reversal point at the end of this subsequent sweep, the wiper is again automatically slowed and the motor maintained at its slow speed during the passage of the wiper through the reversal point, the motor again being returned to its high speed for the next sweep of the wiper across the windscreen. Thus, throughout the high speed mode of operation of the motor, automatic sequencing to low speed adjacent the direction reversal points of the windscreen wiper is accomplished by effective, yet economic, means as provided by this invention.

The present invention will now be described in greater detail and by way of example only, with reference to the accompanying drawing.

In the drawing, there is shown a two-speed motor M for operating one or more windscreen wipers of a motor vehicle, the motor M having a low speed supply brush 1, a high speed supply brush 2, and a common brush 3 connected to ground.

Mounted so as to be rotated with or by the armature of the motor M, is a gear wheel in an associated windscreen wiper arm drive chain (not shown) operatively connected with a control disc 8 which is of electrically insulating material and one of whose circular faces is provided with electrically conductive tracks 9, 10, 11, 12. These tracks 9 to 12 are electrically connected to each other. The innermost track 9 is a ground track connected directly to ground and is of only very short angular extent, as shown in the Figure. The next track 10 is an electrically continuous annulus. The next outer track 11 has an electrically conductive sector 11' which extends over the greater part of the annular extent of the track, and an electrically non-conductive sector 11'' which is of relatively short annular extent. The outermost track 12 is divided into four sectors arranged in two pairs 12', 12'', each sector of the first pair 12' being electrically conductive and of greater annular extent and each sector of the second pair 12'' being electrically non-conductive and of lesser annular extent. The sectors 12', 12'' alternate with each other around the track 12.

Each track 9 to 12 is contacted by a stationary conductive finger, such as the finger 13, which runs on the track 12 as the disc 8 rotates. Each finger is connected to a respective electrical conductor by which the respective track is further connected to other components of the circuit.

Track 10 on the disc 8 is connected by a line 14, including a switch S2, to an on/off relay R2 for starting and stopping the motor M. The track 11 on the disc 8 is connected to a line 16 for supplying a motor speed control relay R1 with 12 volts from the 12 volt vehicle power supply. The outermost track 12 on the disc 8 is connected by a line 19, including another switch S1, to the motor speed control relay R1.

In operation, and with switch S2 closed, the motor M is de-energised. Upon opening of the on/off switch S2, the on/off relay R2 is de-energised and connection is made from the 12 volt vehicle supply line via the normally closed contact 6 of the relay R2 and signal line 15 to the normally closed contact 4 of the speed control relay R1 and the line 17 to the low speed motor supply brush 1. The motor M thus commences rotation at its low speed with the control disc 8 rotating concurrently therewith. Windscreen wipers operatively connected with the motor armature are, thus, driven through forward and reverse wiping motions (sweeps) at the low speed setting.

In order to drive the windscreen wipers at the high speed setting, the high/low speed control switch S1 is also closed in order to energise the high/low speed control relay R1, such that the motor M is then supplied from the 12 volt line via the relay R2 as before, signal line 15, the normally open contact 5 of the speed control relay R1 and line 18 to the high speed motor supply brush 2. The motor M is then operated at high speed, so long as the line 19 has its associated finger 13 running on one of the electrically conductive sectors 12' of the outermost track 12 of the control disc 8.As the disc 8 rotates with the motor M, the finger 13 passes from the electrically conductive sector 12' to the next, electrically non-conductive sector 12'' at which time the speed control relay R1 is de-energised so that the motor supply reverts to the low speed brush 1. This continues throughout the traverse of the finger 13 along the non-conductive sector 12'', and upon its passing on to the next, electrically conductive sector 12', the speed control relay R1 is again re-energised to switch the motor automatically back to high speed.

This alternation between high speed and low speed operation of the motor M continues throughout the entire period during which the high/low speed control switch S1 is closed.

The arrangement of the alternating sectors 12', 12'' on the disc 8 is such that this switching from high to low speed occurs as the wipers approach the extremities of their travel (sweep) in both the forward and reverse directions, the low speed mode continuing throughout a short period of time during which the wipers actually reverse direction. After such reversal is completed, and again under control of the track sectors 12'', 12', the motor is automatically switched back to its high speed mode.

In order to cancel operation of the windscreen wipers, the on/off switch S2 is closed in order to energise the on/off relay R2 and connect either the low 1 or high speed 2 motor supply brush, whichever happens to have been energised at the time, to ground via the normally open contact 7 of the relay R2. This provides for dynamic braking of the windscreen wipers.

Because, during the entire time during which the vehicle ignition circuit, and hence 12 volt supply line, is energised, the relay R2 is energised maintaining the line 15 grounded at terminal 7 so long as switch S2 remains closed, the motor M and windscreen wipers are electrically "locked" in position on the windscreen and cannot, therefore, be deflected by, for example, wind.

During normal operation of the windscreen wipers, reversal at the extremities of the respective forward and reverse sweeps is effected in known manner, for example by means of a crank arm mechanism connected to the continuously-running unidirectional motor M.

The motor controller of the present invention thus provides an automatic speed switching motor control circuit which slows down the motor on its approach to the wiper reversal points and hence brings a greater stability of the wipers, avoiding overshoot at the extremities, without the need for complex and costly electronics such as those involving microprocessors and/or logical circuits. The necessary switching action is achieved in the present invention by means of the outermost, interrupted motor high/low speed control track 12 on the control disc 8 and by inclusion of the high/low speed control relay Rl. This is an effective, yet economic, solution.

Whilst the controller of the present invention has been described hereinabove with reference to the currently preferred embodiment thereof, the scope of the present invention is not to be restricted thereto but extends to all such variants as fall within the broadest scope of the invention as set out herein.

For example, the inventive concept of the controller could be employed with windscreen wiper and other motors capable of operating at more than two speeds.

Claims (17)

1. A controller for a two-speed motor having a first supply brush and a second supply brush, the controller comprising a switching device for selectively directing connection from a supply voltage to a desired one of the first and second supply brushes in order to selectively energise the motor at either a low speed or a high speed, and a sequence control device comprising a control track rotatable in synchronism with the motor and arranged to sequence the motor from its high speed to its low speed and back to its high speed at desired intervals in the rotation of the motor, the sequence control device being rendered operative upon operation of the switching device to select high speed energisation of the motor.

2. A controller according to claim 1, wherein the switching device includes an electro-mechanical relay having its normally closed contact connected to the first supply brush of the motor, the first supply brush being a low speed motor supply brush.

3. A controller according to claim 2, wherein the switching device further includes a switch which, when closed, causes energisation of the relay, so that an input signal line thereof is switched to a normally open contact which is connected to the second motor supply brush, the second supply brush being a high speed motor supply brush.

4. A controller according to claim 2 or 3, wherein the control track of the sequence control device is connected electrically in series with an energisation line of the switching device, in order to de-energise and re-energise automatically the relay of the switching device to provide the specified sequencing of the motor speed.

5. A controller according to any preceding claim, wherein the sequence control device comprises an electrically non-conductive disc which is rotatable by or with the motor and on which the control track is provided, the control track comprising alternating electrically conductive and electrically nonconductive sectors around the track which form a closed geometric figure, such as an annulus.

6. A controller according to any preceding claim, wherein the control track of the sequence control device provides two electrically conductive sectors alternating around the track with two electrically non-conductive sectors.

7. A controller according to any preceding claim including a second switching device having an electromechanical relay with a normally open contact connected to ground.

8. A controller according to claim 7, wherein the second switching device also has an on/off switch.

9. A controller according to claim 8, wherein, when the on/off switch is open, the electro-mechanical relay of the second switching device is de-energised and connection is made from the supply voltage line, through the normally closed contact of the second switching device relay to an output signal line thereof which conducts the supply voltage to the input signal line of the relay of the first-mentioned switching device.

10. A controller according to claim 8 or 9, wherein, when the on/off switch of the second switching device is closed, it causes energisation of the relay thereof to switch its output signal line to its normally open contact connected to ground, thereby causing the associated motor to be dynamically braked to stop.

11. A controller according to claim 10, wherein the sequence control device further comprises a brake track which, when the on/off switch of the second switching device is closed, with consequential energisation of its associated relay, causes one or other of the first and second motor supply brushes to be connected directly to ground, in order to provide said dynamic braking of the motor.

12. A controller for a two-speed motor, substantially as hereinbefore described with reference to the accompanying drawing.

13. A vehicle windscreen wiper system incorporating a two-speed motor which is controllable by a controller according to any preceding claim.

14. A system according to claim 13 when dependent upon claim 5 or any of claims 6 to 12 when dependent upon claim 5, wherein each electrically conductive sector of the control track of the sequence control device of the controller corresponds to a normal sweep of the or each windscreen wiper of the system, whilst each electrically non-conductive sector corresponds to a region of the or each windscreen wiper sweep adjacent its extremity and direction reversal point.

15. A system according to claim 13 or 14 when dependent upon claim 8 or any of claims 9 to 12 when dependent upon claim 8, wherein, when the on-off switch of the second switching device is open, the relay of that device is de-energised and said connection is made from the voltage supply line of the associated vehicle.

16. A system according to claim 13, 14 or 15, when dependent upon claim 10, 11 or 12, wherein said dynamic braking of the motor to stop is arranged to provide consequential dynamic braking to stop of the or each windscreen wiper.

17. A vehicle windscreen wiper system substantially as hereinbefore described with reference to the accompanying drawing.