FIELD OF THE INVENTION

This invention relates to a starter.

In particular, this invention relates to a starter for a vehicle.

BACKGROUND OF THE INVENTION

An internal combustion engine is used as the drive for a vehicle. The crank of the internal combustion engine transfers the reciprocating motion of the crank to a rotational motion of the crank wheel. However, when an internal combustion engine is started the initiation of rotation is done by rotating the crank wheel. The initiation of the crank wheel rotation is done using a starter motor. A starter motor typically consists of a motor comprising a stator and rotor. A gear wheel is coupled to the rotor through a shaft. The stator and rotor may be either permanent magnet/electro-magnets or the like depending on the size of the engine to be started. The changing magnetic field in the stator causes the rotor to rotate, which in turn drives the gear wheel. The gear wheel is adapted to be connected to the crank wheel. The gear wheel of the starter is brought in contact with the crank wheel only when the rotation of the crank wheel has to be initiated.

Many parameters are taken into consideration while designing starters one of them is the number of starts or cranking cycle a starter can withstand before it fails. However, there are various other factors which may lead to starter failure. In view of this invention we will focus on starter failure due to thermal intolerance. The following acts of the vehicle driver lead to starter failure due to thermal intolerance are prolonged cranking when engine fails to start, using starter motor to drive to a safe place in case of engine failure, during a cold start subjecting the starter to draw a very high current in a short time and the like.

A wide range of methods are used to avoid failure of the starter due to thermal issues. One known method is to provide a thermal cut off fuse. The functioning of this fuse is simple, if the temperature to which the fuse wire is subjected increases beyond the rated capacity of the fuse wire due a sudden surge current then the fuse wire bums out. When the fuse wire burns out no current is supplied to the starter thus preventing thermal failure. However, the disadvantage of this method is that unless the fuse is replaced the starter remains unusable thus disabling any means of starting the engine.

Persons skilled in the art will be aware that the component of the starter which is weakest in terms of thermal tolerance is the field winding due to low thermal insulation strength. The commutator of the starter is another component which has low thermal tolerance due to its commutation action. Also, incase the magnets used in the stator and rotor are permanent magnets, the magnets tend to lose their magnetic properties due to thermal intolerance. Thus, thermal intolerance affects various components of the starter.

One popular solution used to overcome the thermal issue, is using a thermal protected starter. In such thermal protected starters, plurality of thermal switches is used in the excitation winding of the starter to protect it from failure. However, one disadvantage of the thermal switches is that while restarting the starter after the starter stops, the time required to dissipate the heat in the field winding is very high. Further, allowing frequent rise in temperature in the excitation winding leads to the degradation in the dielectric strength and loss in thermal insulation of the components of the starter. Also if the starter is subjected to high torque demand from the engine due to a cold start or engine lock condition, then the rise in temperature occurs at a brisk rate. The quick rise in temperature leads to problems such as commutator pitting, quicker brush wears out, armature conductor and insulation failure.

Another method used for thermal protection of the starter is achieved by providing the thermal switch on the brush holder. This method has the advantage that field winding temperature remains low though the rise in temperature is quicker in the brush assembly. However, this reduces effective utilization time of the starter. In such a case the thermal switch can be operated at higher temperature to increase effective utilization time of the starter. But to operate the thermal switch at a higher temperature the size of the thermal switch would have to be increased.

Thus it would advantageous to have a method wherein the rise in temperature is sensed before the temperature reaches a limit which results in the damage of components of the starter. This ensures that the temperature does not reach a level which would damage the starter components. As mentioned before the use of thermal switches is known. One such method of thermal protection of starter is disclosed in the US patent number 5770901. The patent discloses a bimetallic which is used as a thermal switch. As disclosed the bimetallic element is located in proximity of the brush assembly of the starter. When the temperature of the brush assembly increases beyond a threshold value the bimetallic elements stops the flow of current to the brush assembly. Thus any damage to the starter components is avoided.

Typically, the brush assembly of the starter has a temperature threshold which it can handle without being damaged. Also the rise in temperature in the brush assembly is very quick. In such a case there is a possibility that the bimetallic element cuts of the current supply to the starter within the safe temperature operating zone of the brush assembly. If this happens then the starter is switched off forcibly even though the starter could have been operated without getting damaged. Also since the temperature of the brush assembly rises very rapidly the temperature rating of the bimetallic element installed is required to be high which results in increasing the cost of the overall device.

The challenge in designing and implementing a starter device is to provide efficient thermal protection to the starter is by locating the thermal switch in an accurate thermal zone which not only ensures that the starter is not damaged but also ensures that the starter is able to start the engine without being cut off.

It is an object of the invention to provide efficient thermal protection to starter and locating a temperature sensing element in the accurate thermal zone.

ADVANTAGES OF THE INVENTION

The invention as claimed in independent claims has the following advantages. The location of the temperature sensing element in proximity of the wire ensures that the starter is still operable within a safe thermal operating zone without damaging the starter components. Since the temperature sensing element is located in proximity of the wire and the temperature of the wire increases gradually, the temperature rating of the temperature sensing element need not be high. This reduces the cost of the temperature sensing element that is used in the starter in accordance with this invention. This reduces the overall cost of the starter.

Further the location of the temperature sensing element in proximity of the wire ensure that the starter can continue to be operated at a brush temperature which is high but does not damage the brush assembly or any other components of the starter. The location of the temperature sensing elements also ensures that the starter can be operated in a larger temperature range.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:

Figure 1 illustrates a simplified diagram of the starter of a vehicle; and

Figure 2 illustrates a detailed view of one embodiment of the brush holder assembly located in the starter.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 illustrates a starter 10 used in a vehicle to initiate the cranking of the crank wheel in an internal combustion engine. The starter 10 has a housing 11 which houses all the components of the starter 10. The housing houses a stator 13 and rotor 15 pair wherein the rotation of the rotor 15 component is initiated due to the varying magnetic fields generated within the stator 13 and rotor 15 pair. Coils are wound around the laminations in the stator 13 and the rotor 15 which generate the varying magnetic fields. The electricity required to generate the varying magnetic field is provided by a combination of a commutator 17 which is located at one end of the rotor 15. At the other end of the rotor 15 is the gear wheel 19 which engages with the crank wheel of the internal combustion engine. The rotation of the rotor 15 causes the gear wheel 19 to rotate. At least two brushes 14 are located in at least one brush holder assembly 12 form a part of the circuit through which electricity flows from a power source to the brushes 14 to the commutator 17 and finally to the stator 13 rotor 15 pair. The power source is usually a battery. At one end of the fusible braided wire 16 is brush 14 and at the other end of the fusible braided wire 16 a clip 21 is provided which is connected to the battery.

Figure 2 illustrates in detailed a side view of the brush holder assembly 12 in accordance with this invention. In a starter at least one brush holder assembly 12 is provided to mount at least two brushes 14 onto the brush holder assembly 12. Usually the brush holder assembly 12 is made of a non-conductive material. The brushes 14 are the part of the starter 10 which provide the electric connection from the power source to the commutator of the starter. The brushes 14 are located in slots provided in the brush holder assembly 12. The connection between the brushes 14 and the power source is through a wire 16. The wire 16 is a fusible braided wire. A temperature sensing element 18 is located in proximity of the fusible braided wire 16. The temperature sensing element 18 is connected to a controller 20.

The working of the starter 10 with the thermal protection technique employed in accordance with this invention can be explained as follows. When the starter is assembled and ready for operation a physical connection is provided between the clip connected to the fusible braided wire 16 and the battery. When the internal combustion of a vehicle has to started, the user turns the key to crank the engine. When the key is turned there is a flow of electricity from the battery to the brushes 14 of the starter 10 through the fusible braided wire 16. The flow of electricity increases the temperature of the fusible braided wire 16. The temperature of the brushes 14 rises at a quicker pace that the temperature of the fusible braided wire 16. However, the temperature of the brushes is still within the limit such that the brushes 14 are not damaged. The temperature sensing element 18 which is located in proximity of the fusible braided wire 16 senses the temperature of the fusible braided wire 16. The controller 20 monitor this temperature if temperature of the fusible braided wire 16 is above a threshold temperature value then the starter operation is stopped. When the temperature of the fusible braided wire 16 returns to a value which is within the allowable range the starter operation is resumed.

Depending on the number of starting cycle that the starter 10 is subject to the controller 20 can be reconfigured to take care that the starter does not fail due to thermal problems. This increases the life and efficiency of the starter.

One of the advantages of locating the temperature sensing element 18 in proximity of the fusible braided wire 16 is that since the temperature of the fusible braided wire 16 increase less rapidly than the temperature of the brushes 14, it is possible to operate the starter for a longer duration. Further the heat dissipation from the fusible braided wire 16 is quicker than the heat dissipation from the brushes 14. Hence it is possible that the after the starter operation is halted, the starter operation can be resumed much quicker. Thus by locating the temperature sensing element 18 in proximity of the fusible braided wire 16 it is possible to extend the operating range of the starter without comprising the starter efficiency and life.

Another advantage of the locating the temperature sensing element 18 in proximity of the fusible braided wire 16 is that since the temperature rise in the fusible braided wire 16 is gradual the temperature rating of the temperature sensing element 18 that can be used is lower. Thus a temperature sensing element 18 of a lower temperature rating can be used. This reduces the cost of the temperature sensing element 18 and the overall cost of the starter10.

It must be understood that the embodiments explained hereinabove are only illustrative and do not limit the scope of the invention. Many changes and modification in the preferred embodiment are envisaged and fall within the scope of this invention. The scope of this invention is only limited by the scope of the claims.

WE CLAIM:

1. A starter (10) comprising at least one brush holder assembly (12), said at least one brush holder assembly (12) comprising at least two brushes (14) and a wire (16) adapted to connect said at least two brushes (14) to a power source, Characterized in that

(i) a temperature sensing element (18) located in proximity of said wire (16) adapted to sense temperature of said wire (16); and

(ii) a controller (20) adapted to receive temperature information from said temperature sensing element (18) and halt operation of said starter (10) if sensed temperature is above a threshold temperature value.

2. The starter (10) as claimed in claim 1, wherein said controller (20) is adapted to resume operation of said starter (10) after starter (10) operation is halted if temperature sensed is below said threshold temperature value.

3. The starter (10) as claimed in claim 1, wherein said wire (16) is a fusible braided wire (16).

4. The starter (10) as claimed in claim 1, wherein said temperature sensing element (18) is at least one chosen from a group of temperature sensing elements (18) such as bimetallic element, thermostat, positive temperature coefficient element and the like.

5. The starter (10) as claimed in claim 1, wherein said temperature sensing element (18) is externally attached to said wire (16).

6. The starter (10) as claimed in claim 1, wherein said temperature sensing element (18) is integrated to said wire (16).

7. A method of providing thermal protection to a starter (10) in a vehicle, said method comprising the following steps:

(i) switching on the starter;

(ii) sensing temperature of a wire (16) in said starter (10);

(iii) halting starter (10) operation if temperature sensed is above a threshold temperature value;

(iv) sensing temperature of said wire (16) in said starter (10); and

(v) resuming starter (10) operation if temperature sensing is below said threshold temperature value.

8. The method as claimed in claim 7, wherein controller (20) engages or disengages the temperature sensing element (18) located in proximity of the wire (16).