This invention relates to a thermal overload protection system for the starter motor of an iC engine, more particularly, though not exclusively, for the starter motor of the engine of a motor vehicle.
The system proposed herein safeguards the starter against abusive over cranking conditions which usually results in a rise in temperature to an extent damaging the starter motor.
Normally, the firing time of an IC engine is within a second regardless of the capacity of the engine
During normal cranking, the starter motor operates within the acceptable temperature range.
In certain cases, two situations are encountered:
(i) the operator has to resort to continuous cranking
since no firing takes place, (ii) continuous cranking takes place even after the
engine commences to fire by reason of a fault
in the firing circuit or mechanism

In either case, there is always the risk of the starter motor getting burnt out leading to expensive repairs and considerable inconvenience to the user.
This invention therefore has the objective of eliminating the above drawbacks of the known starter of the \C engine.
There Is easy access to the thernrial switch Incorporated in this invention just as easy access to other parts of the engine.
Sufficient cooling Is enabled between cranking efforts by reason of the time delay characteristics of the thernnal switch.
This invention will now be described with reference to the accompanying drawing which Illustrates, by way of example, and not by way of limitation, one of possible embodiments of the proposed system In the single Figure depicted therein.
We have conducted trials and have identified the brush gear plate of the starter motor brush assembly where the carbon brush under high current slides on the commutator segments and generates considerable heat.
A thermal switch is connected to the starter motor through a relay and a solenoid switch,.

The thermal switch has a thermal sensor for sensimg the temperature at the brush assembly, that is, at the brush gear plate, of the motor.
Whenever the temperature of the heat generated at the brush assembly rises above a predetermined temperature, the sensor senses the rise in temperature and actuates the thermal switch to switch off the power supply to the relay and to the solenoid switch to result in the power to the starter being switched off; and whenever the temperature of the heat generated at the brush assembly falls to or below the predetermined temperature, the sensor senses the fall in temperature and actuates the thermal switch to switch on the power supply to the relay and to the solenoid switch to result in the power to the starter being switched on. This operation protects the said motor against thermal overload.
Power is derived from the battery of the vehicle and supplied through the ignition switch. The relay (a safety relay) operates in a very low current range through the thermal switch. The relay energizes the solenoid switch which actuates the starter motor.
There is a time interval between the off and on conditions of the thermal switch, that is, between disconnection and re-connection stages, enabling the said switch to cool down between off and on states. In other words, once the thermal switch is off, re-connection of

the circuit does not take place through the said switch until the said time interval lapses.

WE CLAIM:
1. A thermal overload protection system for the starter motor of an IC engine comprising means for sensing the temperature at the brush assembly of the said motor and for switching off or on the power supply to the starter, whenever the temperature of the heat generated at the brush assembly rises above or falls to or below a predetermined temperature, the said means providing a time delay between switching off and on states.
2. A thermal overload protection system for the starter motor of an IC engine as claimed in Claim 1 wherein the said means consist of a thermal switch connected to the starter motor through a relay and a solenoid switch, said thermal switch having a thermal sensor for sensing the temperature at the brush gear plate assembly of the said motor and thus for actuating the thermal switch to switch off or switch on the power supply to the relay and to the solenoid switch, whenever the temperature of the heat generated at the brush assembly rises above or falls to or below a predetermined temperature, the said thermal switch providing a time delay between its switching off and on states.
3.A thermal overload protection system for the starter motor of an IC engine substantially as herein described with reference to, and as illustrated in, the accompanying drawings.