CLIAMS:We claim,
1. A thermal protection assembly (10) for a starter motor (100), said thermal protection assembly (10) comprises a thermal protection switch (30) having a polymeric sealing (40),
? said thermal protection switch (30) is mounted between a brush plate (20) and a commutator-end-shield (35) of said starter motor (100) such that said polymeric sealing (40) protrudes through a cut-out section of said commutator-end shield (35).
2. The thermal protection assembly (100) of claim 1, wherein said thermal protection switch (30) is mounted on said brush plate (20) at a location proximate to a junction of at least one brush lead.
3. The thermal protection assembly (100) of claim 1, wherein said thermal protection switch (30) cuts off power supply to the starter motor (100) upon detecting overheating of said brush plate (20).
4. The thermal protection assembly (100) of claim 1, wherein said cut-out section has predetermined shape to provide rotation-lock to said thermal protection assembly (100).
5. The thermal protection assembly (100) of claim 1, wherein said polymeric sealing (40) has at least one wiring channel (45) for accommodating at least one wire connected to a relay (5).
6. The thermal protection assembly (100) of claim 1, wherein the polymeric sealing (40) provides water-proof sealing to the thermal protection switch (30) and said at least one wire.
7. The thermal protection assembly (100) of claim 1, wherein the polymeric sealing (40) is a rubber sealing. ,TagSPECI:Field of the invention:
[0001] The invention relates to a thermal protection assembly for a starter motor. More particularly, it relates to mounting assembly of a thermal protection switch in a compact sized starter motor.
Background of the invention:
[0002] Starter motor is an important component of an automotive electrical system. The starter motor gets heated up during its operation and also due to the hot vehicle environment. Power supply to a field coil and brushes of the starter motor is stopped by a thermal switch upon detecting overheating of the starter motor as a protective measure.
[0003] Some models of the starter motor employ ECU to cut-off power supply during overheating condition to provide thermal protection. Although this solution is reliable, it is expensive.
[0004] In other models, a thermal switch is mounted on the brush plate of the starter motor using a long mounting bracket and a rivet. This mounting arrangement requires a lot of space and number of components. Assembly process is more complicated, as the number of sub components is more. Further, because of the vibration, the switch contacts get broken too often.
Brief description of the invention:
[0005] The invention discloses a thermal protection assembly for a starter motor. The thermal protection assembly comprises a thermal protection switch having a polymeric sealing e.g. a rubber sealing. The thermal protection switch is mounted between a brush plate and a commutator-end-shield of the starter motor such that the polymeric sealing protrudes through a cut-out section of the commutator-end-shield.

[0006] The thermal protection switch is mounted on the brush plate at a location proximate to a junction of one or more brush leads. The thermal protection switch cuts-off power supply to the starter motor upon detecting overheating of the brush plate.
[0007] The cut-out section of the commutator-end-shield has a predetermined shape to rotation-lock feature to the thermal protection assembly, that is, the shape of the cut-out prevents unintended rotation of the thermal protection assembly.
[0008] The polymeric sealing has one or more wiring channels for accommodating one or more wires connected to a relay. The polymeric sealing encloses the thermal protection switch and provides water-proof sealing to the thermal protection switch and the wires.
Brief description of the accompanying drawings:
[0009] An embodiment of the invention is described with reference to the following accompanying drawings,
[00010] Fig. 1 shows a perspective view of a starter motor, in accordance with an embodiment of the invention;
[00011] Fig. 2 shows a side view of a thermal protection assembly of a starter motor, in accordance with an embodiment of the invention; and
[00012] Fig. 3 shows a schematic circuit diagram of a thermal protection switch of a starter motor, in accordance with an embodiment of the invention.
Detailed description of the embodiments:
[00013] Fig. 1 shows a perspective view of a starter motor, in accordance with an embodiment of the invention. The starter motor 100 comprises a field coil for generating magnetic field. Power is supplied to the field coil through a set of brushes by a relay 5, which is otherwise called as a solenoid 5. The brushes are mounted on a plate which is called as a brush plate. A thermal protection assembly 10 of the present invention is an arrangement/assembly for mounting a thermal protection switch in the starter motor 100. The assembly 100 will be explained in detail using figure 2.
[00014] Fig. 2 shows a side view of a thermal protection assembly of a starter motor, in accordance with an embodiment of the invention. The thermal protection assembly 10 comprises a thermal protection switch 30 having a polymeric sealing 40. The thermal protection switch 30 is mounted between the brush plate 20 and a commutator-end-shield 35 of the starter motor 100 such that the polymeric sealing 40 protrudes through a cut-out section of the commutator-end-shield 35.
[00015] In an embodiment of the invention, the polymeric sealing is a rubber sealing 40.
[00016] The thermal protection switch 30 is mounted on the brush plate 20 at a location proximate to a junction of one or more brush leads. As the thermal protection switch 30 is mounted close to the welding junction of the brush leads, overheating or the abrupt temperature rise of the brush plate 20 due to brush lead temperature and also overheating of the starter motor 100, is detected more reliably and quickly.
[00017] Upon detecting the overheating of the brush plate 20, the thermal protection switch 30 cuts off the power supply to the starter motor 100. The working of the thermal protection switch 30 is further explained with respect to Fig. 3.
[00018] Fig. 3 shows a schematic circuit diagram of a thermal protection switch of a starter motor, in accordance with an embodiment of the invention. A relay 5 is connected to a power supply line (PS) through a thermal protection switch 30. The relay 5 gets magnetized by the power supplied through the thermal protection switch 30 to close a switch (S1) connected to a starter motor 100. The starter motor 100 gets power supply through the switch (S1) from the power supply line (S1) when the relay 5 is activated.
[00019] In an embodiment, the thermal protection switch 30 is a bimetallic switch 30. The bimetallic switch 30 has a bimetallic disc, which changes its shape (for example, it takes convex shape) when the temperature of the brush plate 20 reaches a first threshold value. In an example, the threshold value can be in the range of 125-135DegC. As a result, the contact of the bimetallic switch 30 gets opened to cut-off power supply to the relay 5. As the relay 5 gets deactivated, the switch (S1) is changed into open condition to cut-off the power supply to the starter motor (100).
[00020] When the temperature of the brush plate 20 is reduced to a second threshold value (for example, 110-120DegC), the bimetallic disc retains its original shape, thereby the contacts of the thermal protection switch (30) get closed to provide power to the relay 5. As a result, power supply to the starter motor 100 through the switch (S1) is resumed.
[00021] The thermal protection switch 30 responds to the overheating of the brush plate 20 and the starter motor 100, more quickly. Thus, the thermal protection switch 30 cuts-off the power supply to the starter motor 100 upon detecting the overheating of the brush plate 20. As a result, failure of the starter motor 100 due to overheating is avoided reliably without the need for expensive electronic circuits such as electronic controller. Further safety is improved.
[00022] Referring back to Fig. 2, the thermal protection switch 30 is sandwiched between the commutator-end-cover 35 and the brush plate 20. The commutator-end-cover 35 has a cut-out section of predetermined shape (e.g. square, rectangle, etc.) to provide rotation-lock to the thermal protection assembly 100. The polymeric sealing 40 of the thermal protection switch 30 also has a similar shape as that of the cut-out section so that, the polymeric sealing 40 of the thermal protection switch 10 protrudes through the cut-out section after the mounting and the assembly process.
[00023] The polymeric sealing 40 acts as an interface between the thermal protection switch 30 and the commutator-end-cover 35. The polymeric sealing 40 withstands the pressure and the forces incurred during the assembly process. Further, the polymeric sealing 40 has one or more wiring channels for accommodating one or more wires connected to the solenoid/relay 5.
[00024] The polymeric sealing 40 provides water-proof sealing to the thermal protection switch 40 and the wires. Hence problems due to moisture and water entry, etc. are avoided reliably. This feature enables the use of the starter motor 100 in agricultural vehicles, tractors, etc. where the starter motor is more prone to water entry.
[00025] The thermal protection assembly 10 requires very less space, hence it is well suited for small-sized starter motor 100 such as a starter motor used for three-wheelers. The assembly 100 offers reliable thermal protection and hence improves safety.
[00026] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.