FIELD OF THE INVENTION

This invention relates to a timing device for a starter of 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. Failure of the starter due to thermal intolerance occurs due to 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. Another cause of starter failure results from mechanical damage to the starter caused due to pinion wear out/damage which occurs due to re-cranking during engine ON condition. Starter failure due to damage to commutator or commutator bursting may occur due to overrunning starter after engine starts. For the purposes of this invention we will focus on starter failures occurring due to thermal intolerance.

A wide range of methods are used to avoid failure of the starter due to thermal issues. One known method is to provide a starter safety relay. A starter safety relay is a very simple electromagnetic device. When the driver of the vehicle turns the key to crank the engine the coils of the starter safety relay energize. The energization of the coils induces a magnetic field from the primary winding to a secondary winding. The contacts of the relay close due to the induced magnetic field and allow the starter to function. The starter safety relay does not ensure that the current flowing to the brushes and the field winding of the starter does not increase beyond a limit which causes thermal failure of the starter. However, the use of a starter safety relay is only able to keep the starter is non operational when the engine is already on. It also does not ensure that in case the starter has been subjected to prolonged cranking, the starter should be allowed to cool down before re-cranking.

Another known method is a starter safety algorithm is implemented in the vehicle electronic control unit (ECU). The starter safety algorithm is programmed such that the starter can be operated for a specific duration of time after which the starter is automatically switched off, for example a program may be such that starter is allowed to function continuously for certain time period after which the starter is switched off for certain time period. One disadvantage of this method is that since this is controlled by an ECU, if the ECU is reset then the timing is lost. In this case the driver of the vehicle is able to operate the starter even if the thermal condition of the starter is such that it may damage the starter. Further, since the current drawn by the starter is proportional to the engine overload, this would to heavy current flow demand and quick rise in temperature leading to thermal failure of the starter.

It is an object of the invention to overcome the disadvantages of the aforementioned conventional techniques, wherein a starter safety relay or a ECU based programming technique is used to protect the starter against thermal failure.

Another object of this invention is to provide a mandatory cool off period to the starter if the temperature of the thermally sensitive components of the starter is above a threshold temperature limit.

ADVANTAGES OF THE INVENTION

The timing device as claimed in the independent claims has the following advantages. The capacitance of the capacitive circuit is representative of the temperature of the thermally sensitive components of the starter. Thus the decrease in capacitance of the capacitive circuit is representative of the decreasing temperature of the thermally sensitive components of the starter. Hence, the capacitance of the capacitive circuit in combination with the controller is able to predict the temperature is within a threshold temperature value which will not damage the starter due to thermal intolerance. This increases the overall life of the starter.

This device and method of this invention, also ensures that the driver of the vehicle is not able to forcefully operate the starter if the temperature of the thermally sensitive elements is above a threshold limit. This results in increase in life of the starter.

The starter on and off is dependent on the capacitance of the capacitive circuit and not on the controller programmed input. This has the advantage that even if the controller is reset the time period for which the starter should be on or off is not lost from the controller memory. This ensures that no false cranking of the starter can occur either when the engine is already running or during the starter cool off period.

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 block diagram of the starter of a vehicle with the timing device; and Figure 2 illustrates the timing device of the starter.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 illustrates a timing device 10 which is connected to the starter 12 of a vehicle. The timing device 10 comprises capacitive circuit 14 and a controller 16. The capacitive circuit stores voltage during the cranking of the vehicle and discharges the stored voltage if the engine does not crank after a threshold time limit. The controller 16 of the timing circuit 10 is adapted to check the residual voltage in the capacitive circuit 14. Based on the residual voltage in the capacitive circuit 14, the controller 16 determines the time period for which the starter has not been in operation. One terminal of the capacitive circuit 10 is connected to the controller 16 while the other terminal of the timing device 10 is connected to the ON terminal of the starter. The controller 16 is also connected to the starter 12. The controller 16 is adapted to receive information from the starter 12 to check if the driver has turned the key to crank the engine.

Figure 2 illustrates the timing device 10. The capacitive circuit 14 is an RC network. The capacitive circuit 14 can be divided into two circuits a capacitive charge circuit 14a and a capacitive discharge circuit 14b. The capacitive charge circuit 14a comprises a terminal which is connected to the starter ON terminal of the starter 12. The capacitive charge circuit 14a further comprises a diode D which is in series connection with the capacitive element 18. The capacitive discharge circuit 14b comprises a terminal which is connected to the controller 16. The capacitive discharge circuit 14b further comprises the capacitive element 18 which is in parallel to a resistive element R.

The working of the timing device 10 can be explained as follows. When the driver of the vehicle turns of the key of the vehicle to crank the engine, the controller 16 first determines the capacitance of the capacitive element 18 of the starter 12, which discharges through the capacitive discharge circuit 14b. If the capacitance of the capacitive element 18 is lower that the threshold capacitive value which is stored in controller 16, then starter 12 is allowed to crank the engine for a predefined time period. During the predefined time period the capacitive element 18 charges. The capacitance of the capacitive element 18 is carefully mapped to the temperature of the thermally sensitive elements. Thus the capacitance of the capacitive element 18 during the predefined time period is representative of the temperature of the thermally sensitive elements of the starter 12. After the predefined time period the starter operation is halted. The capacitive element 18 discharges through the capacitive discharge circuit 14b after the starter operation is halter. The controller 16 monitors the capacitance of the capacitive element 18, when the starter operation is halted.

Until the capacitance of the capacitive element 18 is below the threshold value, the starter operation is terminated.

The design of the timing device 10 of the starter 12 is such that, by terminating the starter 12 operation when the capacitance is above a threshold value provides a mandatory cool off time period to the components of the starter. Further, the mandatory cool off time period ensures that there is no possibility of switching on the starter 12 forcefully even if the drivers of the vehicle turns the key without knowing the thermal state of the starter 12.

Another advantage of the timing device is that the discharging of the capacitive element 18 of the starter 12 is independent of the controller 16. Hence, there is no possibility of the starter operation being resumed even if the driver of the vehicle resets the controller by turning the key of the vehicle completely off. Even if the driver of the vehicle turns the key completely off resetting the controller 16, after the controller 16 is switched on, it first checks the capacitance of the capacitive element 18 to check if the starter operation should be allowed or should be continued to be terminated or suspended.

Another advantage of the timing device is the use of the timing device while starting the engine during heavy load condition of the starter. During heavy load condition of the starter the current drawn by the starter is much higher than the current drawn during normal cranking operation of the starter. Consequently the increase in temperature of the critical component of the starter is also faster in case of heavy load condition. Also in case of heavy load condition there is greater proportional variation in the battery voltage due to load current, thus by sensing battery voltage it is possible to determine the amount of battery voltage required to start the starter in a high load condition. The battery voltage thus can indirectly predict the variation in load current. Hence, it is possible to check the battery voltage to determine the variation in load current. This functionality can be combined with the timing device vary Starter ON & OFF time proportional to the starter load variation to determine whether the starter operation can be altered or the starter operation should be resumed after capacitor has discharged.

Another advantage of the timing device is the use of the timing device while starting the engine during heavy load condition of the starter. During heavy load condition of the starter the current drawn by the starter is much higher than the current drawn during normal cranking operation of the starter. Consequently the increase in temperature of the critical component of the starter is also faster in case of heavy load condition. Also in case of heavy load condition there is greater variation in the battery voltage as the amount of battery voltage required to start the starter in a high load condition is higher. The battery voltage thus can indirectly predict the variation in load current. Hence, it is possible to check the battery voltage to determine the variation in load current, this functionality can be combined with the timing device to determine whether the starter can be operated or the starter operation should be resumed after capacitor has discharged.

It must be understood that the preferred embodiment of the invention as shown in figure 2 is only illustrative and does not limit the scope of the invention. The scope of the invention is only limited by the scope of the claim. Many changes and modification in the components and devices used in the preferred embodiment are envisaged and are within the scope of this invention.

WE CLAIM:

1. A timing device (10) for a starter (12) comprising a capacitive circuit (14) and a controller (16), said capacitive circuit (14) adapted to store voltage during cranking of an engine; said capacitive circuit (14) adapted to discharge said stored voltage if engine does not crank; said controller (16) adapted to check residual voltage in said capacitive circuit (14) and based on value of residual voltage, determine time period for which starter (12) is not in operation.

2. The device as claimed in claim 1, wherein said capacitive circuit (14) comprises a capacitive charge circuit (14a) and a capacitive discharge circuit (14b).

3. The device as claimed in claim 1 and 2, wherein said capacitive charge circuit comprises at least a diode (D) and a capacitive element (18).

4. The device as claimed in claim 1 and 2, wherein said capacitive discharge circuit (14b) comprises at least said capacitive element (18) and a resistive element (R).

5. A method to determine starter (12) operation, said method comprising the following steps:

(i) a controller (16) receiving signal from said starter (12) in response of a driver of vehicle turning a key;

(ii) said controller (16) measuring capacitance of a capacitive circuit (14);
(iii) allowing starter (12) to operate if capacitance of said capacitive circuit (14) is below a threshold capacitance value; and

(iv) terminating starter (12) operation until capacitance of capacitive circuit is below said threshold capacitance value.

6. The method as claimed in claim 5, wherein capacitance of said capacitive circuit (14) is representative of the temperature of the thermally sensitive element of said starter (12).

7. The method as claimed in claim 5, wherein said controller compares the measured capacitance of said capacitive circuit with a threshold value stored in the controller (16).