This invention relates to a device for preventing
chattering resulting from operation of the linkage
of a self parking automotive windscreen wiper
system.
In a wiper motor the armature gets energized on application of DC voltage to the terminals and rotates converting electrical energy to mechanical energy. The rotation of armature drives the reduction gear and in turn, the linkages to get oscillatory motion of wiperf blades,
i
These motors are of self parking type. Although
the DC voltage to the motor is switched off from
the steering column switch, the DC voltage
continues to be available to the motor through sliprings till the wiper blades reach the parking

position of the windscreen and stop in NORMAL conditions. However, in heavy snow conditions, park contacts start chattering due to bouncing
i
back of wiper blades on impacr with snow accumulated under the blades on the windscreen. This invention relates to a device to prevent chattering in snow conditions. Chatter protection
is required when the wiper blades are prevented from parking when snow builds up on the windscreen. The motor is still able to reach its
!
parking position due to operation of system
linkage and stops only on reaching its park position. However, spring energy stored in the system will try to reverse drive the motor gear shaft to realign the linkage to reduce the strain.

If this occurs with a conventional wiper, the motor is electrically energised due to closure of slipring contacts again and driven in the forward direction, but because the wiper blades are still blocked by the snow, the reverse drive cycle due to spring energy and forward cycle due to electrical energisation will repeat - the frequency of which can be faster than one cycle per second. This occurrence damages the system components.
This invention intends to eliminate or at least greatly minimise the drawbacks of the conventional system outlined above and with this in view proposes a device for preventing chattering resulting from operation of the linkage of the self-parking automotive windscreen wiper system, comprising

a control switch connected to the motor of the said system; means for sensing the back e.m.f. of the motor to trigger said control switch whenever said motor is switched OFF to enable said motor to reach its PARK position by providing power supply through control switch, said control switch, when so triggered, turning OFF power supply to said motor, when parking position is reached thus totally de-energising said motor to prevent chattering; a timer for switching OFF power supply to said motor through said control

switch over a pre-determined interval of time, after said motor is powered through said control switch to take the wiper arm to park
■ ■ r
position to prevent continuedjstalling of motor as a result of the movement of the wiper blades being impeded by accumulation of snow on the windscreen during snow fall at any intermediate position other than park position of wiper arm. The control switch may take the form of a relay, an electronic switch, such as, a MOSFET or JGBT.
This invention will now be described with reference to the accompanying drawings, the single Figure in which illustrates by the way of

example and not by the way of limitation, the circuit diagram of one of possible embodiments of the device proposed herein.

When the wiper motor W is switched off from operating mode to parking mode, motor will continue for a brief duration dne io available
1
kinetic energy and hence backemf of motor will be reflected in the motor terminaJs. Since one of the positive motor terminals is connected to park
terminal, park terminal receives the voltage
I ■
signal corresponding to motor backemf and is used as a trigger to turn on the control switch
which connects ppsitive terminal of motor
to battery B and motor continues to rotate till
parking position is reached. At parking position.

trigger for control swithch C is removed and the
! i
control switch is turned off and the motor stops. Under these conditions even when the spring energy in the wiper system is released and wiper
■
reaches non parking position, inotor will not be energized and chattering will be avoided,
i
Another feature of the invention is to protect the motor from continued stalling when the arras and blades of the wiper system arcs prevented from
i
reaching the parking position |by excessive snow fall after the wiper is turned off. Under this condition, when motor stalls due to excessive snow fall at non parking position of wiper arm, a timer circuit T provided for the purpose will turn off the control switch thus turning off power

supply over a pre-detertmined interval of time to prevent the stalled motor from being damaged by overheating of motor coils.
I
It will be appreciated that various embodiments
I I,
of the device proposed herein are possible without departing from the scope md ambit of this invention.

We claim
1. A device for preventing chattering resulting from operation of the linkage of a self-parking automotive windscreen wiper system comprising a control switch connected to motor of the said system; means for sensing
i
the backemf of the motor to trigger said control switch whenever said motor is switched off, to enable sail motor to reach its park position by providing power supply through control switch, said control switch when so triggered, turning off power supply to said motor when parking position is reached thus totally de-energizing said motor to prevent chattering; a timer for switching off power supply to said

motor through said control switch over a pre-determined interval of time, after said motor is powered through said control switch to take the wiper arm to park position to prevent continued stalling of motor as a result of the movement of the wiper blades being impeded by accumulation of snow on the windscreen during snow fall at any iintermediate position other than park position of wiper arm.
.
2, A device for preventing chattering resulting
trom operation of the linkage of a self-parking automotive windscreen wiper system as claimed in claim 1 wherein the control switch is a relay or electronic switch.

I
3. A device for preventing chattering resulting
from operation of the linkage of a self-
parking automotive windscreen wiper
system as claimed in any one of the
I
. I
preceding Claims wherein) the control switch is a MOSFET or IGBT.
i
4. A device for preventing chattering resulting
from operation of the linkage of a self-
parking automotive windscreen wiper
system substantially as herein described
and illustrated.