Power Supply Device for Electrical Equipment of an Automotive Vehicle

1. Field of the Invention

The present invention relates to a power supply device for electric equipment of an automotive vehicle, such as an engine starter.

2. Description of the Prior Art

FIG. 1 shows a conventional power supply device for an engine starter as an example of a power supply device for electric equipment of an automobile. The power supply device comprises a battery 1 coupled to a starter 2 and a switch 3 at the positive terminal thereof. The battery 1 is grounded at the negative terminal thereof. The starter 2 comprises an electromagnetic switch 21 and a starter motor 22. A fixed contact 21a of the switch 21 is coupled to the positive terminal of the battery 1, while the other fixed contact 21b is coupled to a field magnet coil 22a of the motor 2. A movable contact 21c is moved by an excitation coil 21d coupled to a relay 9. The armature 22d of motor 2 is supplied with electric current through a brush 22b coupled to the field magnet coil 22a and a grounded brush 22c. A constant voltage source circuit 6 coupled to the battery 1 at the positive terminal thereof supplies an operating voltage of perdetermined level to a control circuit 7, which, in response to a starting signal from the switch 3 and an engine rotation signal from an engine rotation sensor 8, controls the making and breaking of relay 9, which includes a relay coil 9a and a usually open conact 9b operated by it.

The operation of the device of FIG. 1 is as follows. When the starter switch 3 is made, control circuit 7 supplies a voltage to relay coil 9a, thereby closing the contact 9b to apply the battery voltage E to the excitation coil 21d. Thus, the movable contact 21c comes into contact with the fixed contacts 21a and 21b to supply the battery voltage E to the starter motor 22. When the starter motor 22 has started the associated engine, the rotation sensor 8 generates a rotation signal, and in response thereto, control circuit 7 stops supplying a voltage to the relay coil 9a to open the contact 9b. As a result, the electromagnetic switch 21 is opened and the starter 2 is stopped.

The conventional power supply device shown in FIG. 1 has following disadvantages. Namely, the voltage E across the positive and negative terminals of the battery 1 varies as shown in FIG. 2: When the switch 3 is made to supply voltage E to the starter 2 at a time point A, a rush current flowing through the starter 2 causes the battery voltage E (which has been at a constant rated voltage E0 before time point A) to fall abruptly to a minimum E1 at a time point B. Thereafter, the voltage E gradually increases as the rotational speed of the starter increases. The voltage drop (E0-E1) due to the rush current is especially severe when the ambient temperature is low: In such cases, the minimum voltage E0 may become as low as 4 V. On the other hand, IC (integrated circuit), etc., utilized in control circuit 7 generally operates at a voltage level of about 5 V. Thus, constant voltage source circuit 6 is designed to apply 5 V to control circuit 7 when it is in proper operation. To maintain the output voltage of constant voltage source circuit 6 at 5 V, the input voltage supplied thereto should be kept within the range of from 6 to 20 V. Thus, when the minimum voltage E0 becomes lower than the lower limit (i.e. 6 V) of the acceptable input voltage range (i.e., 6 to 20 V) of constant voltage source circuit 6, the output voltage thereof applied to control circuit 7 becomes lower than the operating voltage (5 V) of control circuit 7. As a result, relay 9 is turned off before the enginne is started. If this happens, it becomes impossibe to start the engine.

In view of the disadvantage of the conventional power supply device of FIG. 1, Japanese laid-open patent application No. 59-155550 proposes to suppress the operation of the control circuit for a predtermined time interval during the starting of the engine, for the purpose of preventing the above-mentioned malfuctioning of the control circuit which may be caused by the lowering of the battery voltage. This suppression of the control circuit, however, results in a loss of control of the power supply circuit, even if for a short period during the starting of the engine. Thus, troubles may ensue in this period.

Alternatively, provision of a back-up battery or a capacitor of a large capacity for supplying the control circuit with power may be contemplated for the purpose of compensating for the lowering of the battery voltage at the starting of the engine. These measures, however, also have problems with regard to maintenance and durability thereof.

Thus, a main object of the present invention is to provide a power supply device for electrical equipment of an automobile, such as an engine starter, wherein malfunctioning of the control circuit due to a rush current of the electrical equipment (e.g. the rush current flowing through the engine starter when the engine is started) can be effectively prevented.

A further object of the present invention is to provide such a power supply device which can be produced and maintained economicaly.

A still further object of the present invention is to provide such a power supply device which has an enhanced durability.

According to the present invention, a power supply device is provided which includes a battery for supplying a DC voltage to an electric device of an automobile which includes a switching means. For example, the power supply device supplies a DC voltage to an engine starter which includes an electromagnetic switch for making and breaking the current supplied from the battery to the starter motor. The input of a voltage raising circuit means, e.g., a DC-DC converter, of the power supply device is coupled to a terminal of the battery through a starting switch which is in series circuit relationship with the voltage raising circuit means. The output of the voltage raising circuit means, on the other hand, is coupled to the input of a constant voltage source circuit, which, in its turn, supplies a constant operating voltage to a control circuit controlling the making and breaking of the switching means of the electric device. Further, a diode is coupled in parallel with the series circuit of the starting switch and the voltage raising circuit means, to supply the battery voltage to the constant voltage source circuit when the starting switch is opened.

Thus, even if the battery voltage goes below the lowest allowable input voltage level of the constant voltage source circuit due to a rush current flowing through the electric device of an automobile upon starting thereof, the voltage raising circuit means supplies to the constant voltage source circuit a voltage which is above the lowest allowable input level thereof. After the starting switch is opened, the diode supplies to the constant voltage source circuit the battery voltage which is substantially recovered by this time. Consequently, the constant voltage can be stably supplied from the constant voltage source circuit to the control circuit, thereby enhancing the reliability of the power supply device according to the present invention.

The novel features which are believed to be characteristic of the present invention are set forth with particularity in the appended claims. The present invetnion itself, however, both as to its organization and method of operation, will be best understood from the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a circuit diagram of a conventional power supply device for an engine starter of an automobile;

FIG. 2 is a graph showing the variation of the battery voltage of a power supply device for an engine starter before and after the engine is started;

FIG. 3 is a circuit diagram of a power supply circuit for an engine starter of an automobile according to the present invention; and

FIG. 4 is a circuit diagram of another power supply circuit for an engine starter of an automobile according to the present invention.

In the drawings, like reference numerals represent like or corresponding parts or portions.

Referring now to FIG. 3 of the drawings, a first embodiment according to the present invention is described. The power supply circuit of FIG. 3 is similar to the circuit of FIG. 1, except for the provision of DC-DC converter 4 and a diode 5 coupled to the input of the constant voltage source circuit 6. Thus, a positive terminal of battery 1 is coupled, through a switch 3, to a starting signal input terminal of a control circuit 7 and to an input terminal of of a DC-DC converter 4 which is well known in the art and which constitutes a voltage raising circuit means according to the present invention. The output terminal of DC-DC converter 4 is coupled to constant voltage source circuit 6 having an output terminal coupled to the operating voltage input terminal of control circuit 7. Further, a diode 5 is coupled across the positive terminal of battery 1 and the input terminal of constant voltage source circuit 6 in parallel circuit relationship with the series circuit of the starting switch 3 and DC-DC converter 4, the forward direction of diode 5 coinciding with the current from the positive terminal of battery 1 to the input of circuit 6. The output of an engine rotation sensor 8 is coupled to an engine rotation signal input of control circuit 7 having a gounded terminal. An output terminal of control circuit 7 is coupled to a relay coil 9a of a relay 9 having a usually open contact 9b. The engine starter 2 supplied and controlled by the power supply circuit as described above comprises an electromagnetic relay switch 21 and a DC electric motor 22. Switch 21 includes fixed contacts 21a and 21b coupled to the positive terminal of battery 1 and a field magnet coil 22a of motor 22, respectively. Switch 21 further includes a movable or armature contact 21c, and an excitation coil 21d for making the contact 21c. On the other hand, motor 22 comprises, in addition to field magnet coil 22a, a brush 22b coupled to field magnet coil 22a, a grounded brush 22c, and an armature 22d supplied from brushes 22b and 22c.

The operation of the circuit of FIG. 3 is as follows. When the switch 3 is made, control circuit 7 makes the contact 9b of relay 9 by energizing the coil 9a in response to the starting signal applied thereto through starting switch 3 in the form of the battery voltage E. Thus, the coil 21d is energized to make the contact 21c, thereby starting the motor 22. Thereupon, as shown in FIG. 2, due to the rush current through the motor 22, the battery voltage E falls abruptly from the rated voltage E1 to a minimum E0 which may be as low as 4 V. DC-DC converter 4, however, outputs a voltage 1.5 times as great as the input voltage thereof. Thus, even when the battery voltage E drops to about 4 V, the input of constant voltage source circuit 6 is supplied with a voltage within the allowable input voltage range thereof, which is from 6 to 20 V. During the time when the switch 3 is closed, diode isolates the output of converter 4 from the positive terminal of battery 1. On the other hand, when the associated engine (not shown) is started by the motor 22 and switch 3 is opened, the voltage supply to converter 4 is stopped and the output there of drops to zero. Thus, battery voltage E is supplied through diode 5 to constant voltage source circuit 6. Consequently, control circuit 7 is kept on being supplied with a voltage within the operating voltage range thereof.

FIG. 4 shows a second embodiment according to the present invention, which is identical with the circuit of FIG. 3 except for the provision of a transistor 10 coupled in series with the relay coil 9a of relay 9. In the case of the circuit of FIG. 4, the output of control circuit 7 turns on the transistor 10 in response to the starting signal from switch 3 to energize the coil 9a, instead of directly energizing it. Since an output of small current suffices to turn on a transistor, control circuit 7, and hence constant voltage source circuit 6, can be constituted by a a small-sized and economical circuit of a smaller rating.

While particular embodiments of the present invention have been described above, it will be understood that many modifications may be made without departing from the spirit of thereof. For example, the constant voltage source circuit 6 may be dispensed with to couple the output of the converter 4 directly to the operating voltage input of the control circuit 7 without destroying the function of the power supply circuit. Further, the power supply circuit according to the present invention may be utilized to supply and control an electrical device other than the engine starter, e.g. an ignition system of an automobile, to ensure the stable starting operation thereof. The appended claims are contemplated to cover any such modifications as fall within the true spirit and scope of the present invention.