This invention relates to a thermal overload protection system for the starter motor(6) of an IC engine, more particularly, though not exclusively, for the starter motor of the engine of a 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(6) operates within the acceptable temperature range.

In certain cases, two or more of similar 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(6) 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 IC engine.

There is easy access to the thermal cut out 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 thermal cut out.

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 Figures depicted therein.

Fig 1 illustrates a separate view of a brush box with thermal cut out.

Fig 2 illustrates a brush gear assembly

Fig 3 illustrates circuit diagram of the system A thermal cut out Is connected to the starter motor through a relay(4) and a solenoid switch(5).

Fig 1 in Greater Detail

Referring fig 1, the thermal cut out (2) is shown as assembled Inside a cup (1) which is joined to the brush box (11) by weld joint (any other joint is also possible); of the brush gear assembly; the continuous current passing through the carbon Brush generates heat (in the form of temperature rise ) around the brush box, the generated heat will be transferred to the thermal cut out (2) using a heat transfer sheet (3) s silicone rubber material which has a special property to provide electrical insulation and also will transfer the heat from the component to chassis and when temperature exceeds the predetermined limit, the temperature sensor in the thermal cut out senses the temperature an actuates the thermal cut out and thereby disconnects the supply to the relay(4) and the starter motor(6) is de-energized

Fig 2 in Greater Detail:

Referring fig 2, the thermal cut out (2) is shown as assembled inside a cup (1) which is joined to the brush box (11) by screwing it in the brush gear assembly; the continuous current passing through the carbon Brush generates heat (in the form of temperature rise ) around the brush box, the generated heat will be transferred to the thermal cut out (2) using a heat transfer sheet (3) a silicone rubber material which has a special property to provide electrical insulation and also will transfer the heat from the component to chassis and when temperature exceeds the predetermined limit, the temperature sensor in the thermal cut out senses the temperature and actuates the thermal cut out and thereby disconnects the supply to the relay and the starter motor(6) is de-energized

Whenever the temperature rises above a predetermined temperature, the sensor senses the rise In temperature and actuates the thermal cut out and cut off the power supply to the relay (4) and the starter motor (6) is reenergized and whenever the temperature falls to or below the predetermined temperature, the sensor senses the temperature and actuates the thermal cut out to reclose and enables the user to switch on the starter motor(6) if he wishes to do so. This operation protects the said motor against thermal overload.

Power is derived from the battery(7) of the vehicle and supplied through the ignition swltch(8). The relay(4) operates at a very low current range through the thermal cut out. The relay(4) energizes the solenoid(5) which actuates the starter motor(6).

There is a time interval between the off and on conditions of the thermal cut out, that is, between disconnection and re-connection stages, enabling the said cut out to cool down between off and on states. In other words, once the thermal cut out is off, re-connection of the circuit does not take place through the said cut out until some 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 least at one point in the motor circuit, and then for switching OFF the power supply to the motor whenever the temperature sensed rises above a predetermined value, said means not only switching ON the said power supply whenever the temperature sensed falls to or below the said value, but also causing a predetermined time delay interval between every such cessation of the said power supply and its succeeding resumption.

2 A thermal overload protection system as claimed in Claim 1 wherein the said means consist of a thermal cutout incorporating a thermal sensor for sensing the temperature; a relay-solenoid circuit for being actuated by the thermal cutout whenever the temperature of the heat generated rises above or falls to or below a predetermined value, said thermal cutout causing the said time delay between every such cessation of the said power supply and its succeeding resumption.

3 A thermal overload protection system as claimed in Claim 2 wherein the said thermal sensor is placed inside an enclosure attached to the brush box of the said starter motor, said enclosure being made of a heat conductive material including metal.

4. A thermal overload protection system as claimed in Claim 3 wherein the enclosure is attached to the brush box by means including spot welding.

5. A thermal overload protection system as claimed in any one of the preceding Claims wherein the heat generated is transferred to the thermal cutout through a heat conducting member.

6. A thermal overload protection system as claimed in Claim 5 wherein the heat conducting member is a heat transfer sheet.

7. 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.