FIELD OF THE INVENTION

[001] The present invention generally relates to a starter for a motor vehicle, and particularly relates to an inrush current controlling unit incorporated with an electrical circuit of the starter.

BACKGROUND OF THE INVENTION

[002] In typical motor vehicle applications, when an engine associated with the vehicle is cranked to start the vehicle from its static condition, the starting motor that is generally a DC series motor draws in high inrush current before it overcomes the static inertia possessed by the engine of the vehicle and starts rotating the flywheel of the engine. The occurrence of high inrush current is due to the low resistance of the system circuit that is exposed to the full battery voltage at the time of cranking the engine flywheel. The inrush current generally appears for a very small period of time in the order of milliseconds. At his time, the battery voltage drastically drops down below a threshold value, which ultimately affects function of other sensitive electronic items generally used in vehicle. Nowadays, many of the modern vehicles uses various electronic equipments, hence, to have efficient working of all these components, the voltage drop in the battery caused due to the starter has to be limited and controlled. Moreover as automotive applications go green, vehicle design moves towards stop-go kind of practice to limit undesired emissions of exhaust, noise and fuel consumption during conditions of unutilized traction power of the engine. This stringent norms on vehicle engineering, demands enhancement on the starting motor durability in terms of strength and duty cycle to a multi fold, in order to meet the needs and requirements of the modern engines developed for the applications as said above. The life of the starter motor is greatly dependant on the life of the carbon brush which is used to transfer electrical energy to the motor. Inrush current is one of the factors which are responsible for the life of the carbon brush. Increasing demands on the life of the starting motor necessitates the need of reducing the undesired inrush current flowing through the motor.

[003] With advancement in magnet technology, starting motors used in automotives of lower power, have moved from wound field technology to permanent magnets for the generation of magnetic flux. The use of permanent magnets in the motor design has reduced the resistance of the machine which used to be higher for the same power of motor, earlier with wound coil design. This has a direct effect on the machine's characteristics to the input energy. When the machine resistance is reduced the current which is indirectly proportional to the resistance has gone high. As the period of this inrush was very small as said above in the order of milliseconds it had not affected the functionalities in the vehicle system.

[004] Today, because of significant application of advanced electronics, there is a need to have reduced inrush current. Hence, starting motors are found to design with wound field coil to have increased electrical resistance there by to reduce the inrush current drawn. To further limit the inrush, the wound coils are made as two pairs and energized one by one in a phased manner through external relays in addition to the existing solenoid of the starter. By having the coils in separate pair, it was possible to increase the machine resistance and by having dual contact arrangement it was possible to energize the pair of coils one by one during the moment of starting in a phased manner and both the coils at the time of cranking. This arrangement found to have reduced inrush current drawn.

[005] However, arrangement of this type to reduce the inrush current is limited to motors with wound coil design and in addition calls for a dual contact arrangement to achieve this function. The availability of permanent magnets with enriched magnetic characteristics necessitates the need of an inrush limiting system to be used along with efficient magnets in motors.

OBJECT OF THE INVENTION

[006] The present invention overcomes the shortcomings associated with the background art and achieves other advantages not realized by the background art.

[007] The principal object of the present invention is to provide an inrush current controlling unit for reducing inrush current occurring during the starting event of the vehicle and thereby to increase the life of the battery.

[008] Another object of the present invention is to design the inrush current controlling unit that is simply adaptable with the existing starter design without much modification therein.

[009] Yet another object of the present invention is to configure the inrush current controlling unit with the current electrical configuration of the starter without affecting performance of any of the components.

SUMMARY OF THE INVENTION

According to main aspect of the present invention, the starter comprises a motor configured in an engagement relationship with flywheel of an engine, a battery for supplying electrical power to said motor, a solenoid switch for energizing said motor upon actuation of an ignition switch, and an inrush current controlling unit that is electrically connected in parallel to said solenoid switch and in series with the motor. The inrush current controlling unit comprises a resistor having a resistance level equal or less than that that of a primary winding of said solenoid switch, and a diode for restricting reverse flow of current caused due to an emf developed by said motor at the starting event of the vehicle, particularly before a closed circuit is established between an first power cable and a third power cable. Said resistor and said diode are connected in series with each other.

[010] Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[011] The present invention will be better understood fully from the detailed description that is given herein below with reference to the accompanying drawings of the preferred embodiments of the present invention, which, however, should not be deemed to be a limitation to the invention to the specific embodiments, but, are for the purpose of explanation and understanding only.

In the drawings:

[012] FIG.l is a block diagram representing an electrical configuration between a power source and the starting motor in association with the inrush current controlling unit according to the present invention.

[013] FIG.2 is an electrical circuit diagram illustrating electrical relationship among components associated with the starter and the inrush current controlling unit of of FIG.l.

[014] FIG.3 is a graphical representation showing the effect of of current as against the time with the application of inrush current controlling unit of FIG. 1 in the starting motor during the cranking of engine.

DETAILED DESCRIPTION OF THE INVENTION

[015] While this invention is susceptible of embodiments in many different forms, the detailed description of the preferred embodiments with reference to the corresponding drawings shown herein below are to be understood that the present disclosure shall be deemed as an example of the principles of the invention and not intended to limit the invention to the specific embodiments shown and described. In the description below, like reference numerals are used to describe the same, similar or corresponding parts in the several views of FIG 1- 3

[016] Referring to FIG.l, the block diagram shows various components involved in the process of energizing a motor (100), thereby to crank an internal combustion engine (101) of a motor vehicle. The engine (101) has a flywheel that is integrated with a ring gear on outer circumference thereof. The motor (100) has an output shaft coupled with a pinion gear adapted to be configured with the ring gear of the flywheel of the engine (101) to create an engagement relationship between the ring gear and the pinion gear during the event of start of the vehicle. The paramount factor that effect efficient cranking of the engine is the potential difference at which the current is drawn by the motor (100). Hence, the variation in current flow through the motor plays a vital role for better performance thereof during the starting event of the engine at diverse situations such as cold condition, static condition, etc. According to the present invention, this variation in current flow during the starting event of the engine is performed by incorporating an inrush current controlling unit (102) in series connection with the motor (100).

[017] Electrical energy for energizing the motor (100) is received from an electrical power source called battery (103). The battery is generally used for supplying electrical power to various electrical applications of the vehicle, such as lamps, AC, audio system, etc. Hence, demand for a battery in a vehicle is very much significant and maintenance of predefined level of voltage in a battery through out the running of the vehicle for efficient function of electrical appliances is very much essential. As the starting motor is the first component which require electrical power during starting of the vehicle, utmost care should be taken that a threshold voltage level to be maintained in the battery (103). High current during starting event of the engine will cause a significant drop in voltage across the battery. This scenario shall be given least importance when the vehicle moves from its static condition. As this inrush current last for few seconds, that too in milliseconds, it may not affect other electrical appliances. Wherein during the running condition of the vehicle, for example when a stop/start system is used, significant drop in voltage occurs across the battery due to high inrush current. This low voltage my cause poor performance of other electrical appliances.

[018] According to FIG.l, a positive terminal (Bl) of the battery (103) is electrically connected via a first power cable (PI) with a second positive terminal (S2) of a solenoid switch (104). The positive terminal (Bl) of the battery (103) is also electrically connected to a first terminal (IS1) of an ignition switch (105), which is also generally referred as ignition key, via a first control cable (CI). Cross sectional area of the first power cable (PI) is made sufficiently large enough to carry high ampere current to energize the motor (100) wherein cross sectional area of the first control cable (CI) is comparatively smaller than the cross sectional area of the first power cable (PI) to draw low ampere current thereby to take an advantage in the selection of appropriate ignition switch considering the cost thereof and circuit design complexity. A negative terminal (B2) of the battery (103) is grounded via a power cable (P2). A second terminal (IS2) of the ignition switch (105) is electrically connected with a first terminal (IR1) of an ignition relay (106) via a second control cable (C2) and a second terminal (IR2) of the ignition relay (106) is grounded via a third control cable (C3). The ignition relay (106) used in the circuit is a coil type relay which contains four terminals. A third terminal (IR3) of the ignition relay (106) is electrically connected with a fourth control cable (C4) with its first end and second end thereof is coupled with a junction (Jl), wherein a fourth terminal (IR4) is electrically connected with a fifth control cable (C5) with its first end and second end thereof is electrically connected with a first positive terminal (SI) of the solenoid switch (104). When the ignition switch (105) is activated, it establishes a closed circuit between the first control cable (CI) and the second control cable (C2) which in turn establishes a closed circuit loop through the positive terminal (Bl) of the battery (103) and the second terminal (IR2) of the ignition relay (106). As the low ampere current flows through the ignition relay (106), the wound coil get energized and thereby establish a closed circuit between the fourth control cable (C4) and the fifth control cable (C5).

[019] Referring to FIG.2, the solenoid switch (104) comprises a primary winding (Wl) and a secondary winding (W2) which are electrically connected in parallel to each other, wherein the primary winding (Wl) is designed in such a way to possess less resistance compare to the secondary winding (W2). A plunger (107) is disposed in the solenoid switch (104) to establish a close circuit between the second positive terminal (S2) and a third positive terminal (S3), said third positive terminal is connected with a third power cable (P3) with its first end and a second end thereof is electrically connected with a positive terminal (Ml) of the motor (100). A negative terminal (M2) of the motor (100) is grounded via a fourth power cable (P4). As the ignition switch (105) is activated, the low ampere current flows to the solenoid via the first positive terminal (SI) through the ignition relay (106), which energize the primary winding (Wl) to pull the plunger (107), thereby to establish an electrical contact between the second positive terminal (S2) and the third positive terminal (S3). The moment a closed circuit is established between the first power cable (PI) and the second power cable (P3), electrical power from the battery (103) is given to the motor (100) for energizing the motor and thereby to crank the engine (101). The contact is sustained/hold in for some time with the help of a secondary winding (W2) sufficient enough to crank the flywheel of the engine (101). The moment the contact is established between the second and the third positive terminals (S2 & S3), the current flow through the primary winding (Wl) gets cut off, but the current flow through the secondary winding (W2) remains until the ignition switch (105) is deactivated.

[020] Referring to FIG.3, Y-axis represents current flow through the motor (100) during the starting event of the vehicle and X-axis represents the time duration of operation of starter. In the event of typical starter motor operation without the presence of inrush current controlling unit of the present invention, the initial current at time T1 reaches a current level C1, which is generally referred as peak current, and gradually lowers to a current level C2 as the time goes up till T2, then the current fluctuates for some time during the operation of the starter till the ignition switch (105) is deactivated. This peak current C1 drawn by the motor (100) between the times T1 & T2 significantly reduce the voltage level available in the battery.

[021] Referring to FIG.l & FIG.2, the inrush current controlling unit (102) according to the present invention is electrically connected in parallel to the solenoid switch (104) and in series with the motor (100). The inrush current controlling unit (102) comprises a resistor (R) and a diode (D), which are connected in series with each other. It should be understood by a skilled person that a plurality of resistors shall be provided in parallel with the solenoid switch as required with or without significant modification in the preferred embodiment of the present invention, and such modification shall not be deemed as limitation to the scope of the present invention. A first terminal (IU1) of the inrush current controlling unit (102) is electrically connected with a first end of a sixth control cable (C6) and second end thereof is electrically connected with a second junction (J2). A second terminal (IU2) of the inrush current controlling unit (102) is electrically connected with a first end of a seventh control cable (C7) and second end thereof is electrically connected with a third junction (J3). As the ignition switch (105) is activated, the current flows through the ignition relay (106) and then flows through the solenoid switch (104) and the inrush current controlling unit (102). The amount of current flows through the solenoid switch (104) and the inrush current controlling unit (102) depends on the resistance level of the primary winding (Wl) and the resistor (R), respectively. The combined resistance offered by the primary winding (Wl) and the resistor (R) establishes a reduced voltage drop across the motor (100) which in turn draws a current sufficient enough to facilitate rotation of the motor (100) at a speed N1 before the contact is established between the first and the third power cable (PI & P3). Rotation of the motor (100) at the speed N1 develop an emf E1 which oppose the voltage drop across the motor (100) once the contact is established between the first and the third power cable (PI & P3). Hence, the inrush current during the starting event of the vehicle is reduced at desired level by incorporating the inrush current control unit (102) of the present invention. The diode (D) is provided to restrict reverse flow of current caused due to the emf E1.

[022] The selection of resistance level of the resistor (R) plays a crucial role in effective performance of the motor (100) and reduction of inrush current during the starting event of the vehicle. If the resistance level of the resistor (R) is higher than the resistance offered by the primary winding (Wl), then the combined voltage drop across the resistor (R) and the primary winding (Wl) may be high. This voltage drop may not be sufficient enough to rotate the motor (100) at desired speed before the the contact is established between the first and the second power cable (PI & P3). At the same time, there may be tendency that maximum current may pass through the primary winding (Wl) for pulling the plunger 107) and minimum current flow through the resistor (R). This event may not reduce the inrush current as desired. Whereas, if the resistance level of the resistor (R) is lesser than the resistance offered by the primary winding (Wl), then the combined voltage drop across the resistor (R) and the primary winding (Wl) may be less, which may cause rotation of the motor (100) at desired speed before the contact is established between the first and the second power cable (PI & P3), and thereby effective reduction in the inrush current may be achieved. Very low resistance level of the resistor (R) may affect the effective performance of the solenoid switch (104). Hence, to have a better inrush current reduction during starting event of the vehicle and for effective performance of the motor (100), the inrush current controlling unit (102) of the present invention provide the resistor (R) having the low resistance level in comparison with the primary winding (Wl). The selection of rating of resistor (R) and the diode (D) should be deemed within the scope of the present invention as a person skilled in the art may think of different rating of resistor (R) and the diode (D) for various requirements as per the wide applications in the field of starter.

[023] Referring to FIG.3, with the presence of inrush current controlling unit of the present invention in a typical starter, the initial current at time T1 reduced to a current level C3 and gradually lowers to a current level C2 as the time goes up till T2, then the current fluctuates for some time during the operation of the starter till the ignition switch (105) is deactivated. This peak current C3 drawn by the motor (100) between the times T1 & T2 does not reduce the voltage level in the battery beyond a desired threshold voltage. The reduction of inrush current CR from C1 to C3 is the ultimate effect of the inrush current controlling unit (102) of the present invention. The inrush current reduction CR shall be varied to adapt with various application with the inrush current controlling unit (102) of the present invention with or without significant modification, hence, the preferred embodiment disclosed in the foregoing description should not construed as a limitation to the scope of the present invention.

[024] It will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed in the foregoing description. Accordingly, the preferred embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention, which is to be given the full extent of the appended claims.

We claim:

1) An inrush current controlling unit (102) associated with a starter for a motor vehicle, said starter comprises a motor (100) configured in an engagement relationship with flywheel of an engine (101), a battery (103) for supplying electrical power to said motor (100), and a solenoid switch (104) for energizing said motor (100) upon actuation of an ignition switch (105), characterized in that said inrush current controlling unit (102) is electrically connected in parallel to said solenoid switch (104).

2) The inrush current controlling unit (102) according to claim 1 comprising:

a resistor (R) having a resistance offered equal or less than that is offered by a primary winding (Wl) of said solenoid switch (105);

a diode (D) for restricting reverse flow of current caused due to an emf E1 developed by said motor (100) at the starting event of the vehicle, particularly before a closed circuit is established between an first power cable (PI) and a third power cable (P3);

wherein said resistor (R) and said diode (D) are connected in series with each other.