Direction indicator for automobile

[57] ABSTRACT

A direction indicator for automobiles having a negative grounded battery and utilizing semiconductor circuits for the control of two or more sets of lights individually with the lights of each set being operated in sequence or simultaneously to indicate a change in direction of the vehicle and relatively high resistance lights in series with the direction lights to indicate to the driver improper operation of the circuit.

Claims, 3 Drawing Figures

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PATENTED DEC 19· 1972

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DIRECTION INDICATOR FOR AUTOMOBILE

This invention relates to a direction indicator for automobiles, especially to an electronic circuit for operating such a direction indicator, which includes a plurality of laterally arranged electric lamps illuminated sequentially one by one from left to right or from right to left and all the lamps are simultaneously extinguished after the last lamp is illuminated. This operation is then repeated to provide an indication of the travelling direction of the automobile.

Direction indicators of this type have been already used in some automobiles. However, these direction indicators according to the prior art have been operated by sequentially switching a train of mechanical switch contacts of a lamp circuit by means of an electric motor and numerous troubles have been encountered such as mis-illumination and improper illumination of the lamps due to abrasion of the switch contacts or deterioration of the contact springs.

In order to overcome the difficulties of prior direction indicators, an electronic switching circuit has been proposed which utilizes electronic switching elements such as silicon controlled rectifiers (hereinafter referred to as SCR) in place of the mechanical switches and has overcome the difficulties caused thereby. However, the circuit presents difficulties in that its circuit configuration including the indication lamps requires that one terminal of each lamp be connected to the positive terminal of the power supply and the circuit therefore cannot be applied directly to an automobile of negative-grounded type which is now most commonly used.

One object of this invention is to provide an improved direction indicator circuit which is directly applicable to the negative-grounded type automobile.

This object can be attained by providing a circuit comprising a plurality of indication lamps each having one terminal connected to the negative terminal of the power supply in accordance with this invention. In the circuit of this invention, (n — 1) series connections each consisting of an SCR and a lamp connected to the cathode electrode thereof and included in the first through (n — l)th stages of the circuit, and one series connection consisting of an SCR and a resistor connected to the cathode electrode thereof and included in the n-th stage of the circuit are connected in parallel between the positive and negative terminals of the d.c. source. A commutating capacitor is connected between the cathode electrode of the SCR in the first stage and the cathode electrode of the SCR in the n-th stage, and circuits respectively including a capacitor and an impedance element are connected respectively between the cathode electrodes of the SCR’s in the second through (n — 1 )th stages and the cathode electrode of the SCR in the ζι-th stage. The impedance element is selected to have an impedance varying in accordance with the direction of the current passing therethrough.

Other objects and features of this invention will be best understood from the following description with reference to the accompanying drawings.

In the drawings:

FIG. 1 is a circuit diagram of one embodiment of a direction indicator circuit according to this invention;

FIG. 2 is a circuit diagram of a modification of the circuit of FIG. l;and

FIG. 3 is a circuit diagram is still another modification of the circuit of FIG. 1.

Throughout the drawings, like reference numerals are used to denote like circuit elements.

Referring now to FIG. 1, the circuit consists of four stages respectively including three lamps 21, 22, and 23 and a resistor 24. The lamps 21, 22, and 23 are to be attached to the tail of the automobile and controlled by the circuit of this invention for indicating the travelling direction of the automobile. One end of each lamp 21, 22 and 23 and the resistor 24 are respectively connected to the cathode electrodes of four SCR’s 11, 12, 13, and 14, and the other ends thereof are connected in common to the negative terminal 4 of the d.c. source 1. The anode electrodes of the SCR’s 11, 12, 13, and 14 are connected in common to the positive terminal of the d.c. source 1 through a switch 2.

The gate electrode of the SCR 11 in the first stage is connected through a series connection of a capacitor 41 and two resistors 91 and 51 to the positive terminal of the source 1, the gate electrode of the SCR 12 in the second stage is connected through a series connection of a capacitor 42 and two resistors 92 and 52 to the cathode electrode of the SCR 11 in the first stage, the gate electrode of the SCR 13 in the third stage is connected through a series connection of a capacitor 43 and two resistors 93 and 53 to the cathode electrode of the SCR 12 in the second stage, and the gate electrode of the SCR 14 in the fourth stage is connected through a series connection of a capacitor 44 and two resistors 94 and 54 to the cathode electrode of the SCR 13 in the third stage.

The junctions of the capacitor 41 and resistor 91, the capacitor 42 and resistor 92, the capacitor 43 and the resistor 93 and the capacitor 44 and resistor 94 are respectively connected through diodes 31, 32, 33, and 34 to the output terminal 5 of a trigger pulse generator 3, and the junctions of the both resistors 91 and 51, etc., in the respective stages are connected respectively through capacitors 101,102,103, and 104 to the negative terminal 4 of the source 1. The combinations of the resistor 51 and capacitor 101, the resistor 52 and capacitor 102, the resistor 53 and capacitor 103 and the resistor 54 and capacitor 104 respectively constitute filter circuits. The input terminal of the trigger pulse generator 3 is connected to the positive terminal of the source 1.

The cathode electrode of the SCR 11 in the first stage is also connected through a capacitor 61 to the cathode electrode of the SCR 14 in the fourth stage. The cathode electrodes of the SCR’s 12 and 13 in the second and third stages are respectively connected through a series connection consisting of a capacitor 62 and a parallel connection of a diode 72 and a resistor 82 and a series connection consisting of a capacitor 63 and a parallel connection of a diode 73 and a resistor 83 to the cathode electrode of the SCR 14. The SCR’s 11, 12, 13 and 14 have respectively gate leakage resistors 111, 112, 113, and 114 connected between the cathode and gate electrodes thereof.

In operation, the switch 2 is closed to apply an operating voltage from the d. c. source 1 to the respective series connections of the SCR’s 11, 12, 13, and 14 and the lamps 21, 22, and 23 and the resistor 24 and also start the operation of the trigger pulse generator 3.

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At first, all of the SCR’s 11, 12, 13, and 14 are nonconductive and therefore the cathode electrodes of the SCR’s are at a same potential as that of the negative terminal 4 of the source 1. Accordingly, no current flows through the diodes 32, 33 and 34 in the second through fourth stages, while a current flows through the diode 31 in the first stage and through the resistors 91 and 51 and the pulse generator 3.

When a positive trigger pulse is generated from the trigger pulse generator 3 in the above condition, it cancels the current in the diode 31 for the duration of the pulse and therefore, raises the potential at the junction of the resistor 91 and the diode 31, thereby transferring the trigger pulse through the capacitor 41 to the gate electrode of the SCR 11 in the first stage. The first trigger pulse drives the SCR 11 into conduction and illuminates the lamp 21. Due to the conduction of the SCR 11, its cathode potential is raised substantially to the voltage of the source 1. Therefore, a part of the conduction current is filtered by the filter circuit consisting of the resistor 52 and capacitor 102 and flows through the resistor 92 and the diode 32, thereby maintaining the junction of the capacitor 42 and the diode 32 at low potential.

The second positive trigger pulse appearing at the output terminal 5 of the pulse generator 3 in the above condition similarly cancels the current flowing through the diode 32 and therefore raises the potential at the junction of the diode 32 and the resistor 92 for the duration of the pulse thereby transferring the second trigger pulse through the capacitor 42 to the gate electrode of the SCR 12 in the second stage. Thus, the SCR 12 is driven into conduction to illuminate the lamp 22.

In the same manner, the SCR 13 in the third stage is driven into conduction and the lamp 23 is illuminated by the third trigger pulse. Thus, the cathode potentials of the SCR’s 12 and 13 in the second and third stages are substantially raised to the voltage of the source 1 and therefore the commutating capacitors 62 and 63 connected to the cathode electrodes of these SCR’s are charged relatively slowly through the resistors 82 and 83 respectively. The commutating capacitor 61 connected to the cathode electrode of the SCR 11 in the first stage is also charged through the resistor 24.

When the fourth trigger pulse appears, it drives the SCR 14 in the fourth stage into conduction in the same manner as in the case of the SCR 13, and the cathode potential of the SCR 14 is raised substantially to the voltage of the source 1. Therefore, the charges stored in the commutating capacitors 61, 62 and 63 are concurrently discharged and raise the cathode potentials of the SCR’s 11, 12, and 13 above the anode potentials thereof for a predetermined period and cause the SCR’s 11, 12, and 13 to become nonconducting and extinguish all of the lamps 21, 22, and 23. Thus the circuit is restored to its original condition except for the SCR 14 in the last stage.

The SCR 14 is retained in the conduction mode and the cathode potential thereof is nearly equal to the source voltage. Therefore, the commutating capacitor 61 is charged inversely to the above case so that one electrode connected to the cathode electrode of the SCR 14 is poled positive and the other electrode connected to the cathode electrode of the SCR 11 is poled negative. When the next trigger pulse appears with the circuit in this condition, it drives the SCR 11 in the first stage into conduction to illuminate the lamp 21 and discharge the commutating capacitor 61, thereby raising the cathode potential of the SCR 14 above the anode potential thereof and disables the SCR 14.

By repeating the above mentioned operation, the sequential illumination and simultaneous turning off of the lamps 21 22 and 23 is periodically repeated, thereby indicating the travelling direction from left to right, for example.

The diode 72 serves the function of preventing the commutating capacitor 62 from being charged quickly and causing it to be charged slowly through the resistor 82 when the SCR 12 is driven into conduction. Similarly, the diode 73 serves the function of preventing the commutating capacitor 63 from being charged quickly and causing it to be charged slowly through the resistor 83 when the SCR 13 is driven into conduction. However, when the SCR 14 in the last stage is driven into conduction and raises its cathode potential, the three commutating capacitors 61, 62, and 6.3 are concurrently discharged. Thus the capacitors 62 and 63 are charged only through the resistors 82 and 83 and discharged only through the diodes 72 and 73, respectively. Therefore, it is necessary to provide a charging time for the capacitors 62 and 63 sufficiently longer than the discharging time thereof and the values of the resistors 82 and 83 are therefore relatively large.

If the diodes 72 and 73 were not inserted, only one SCR could conduct at a time. In other words, for example, if the SCR 12 is driven into conduction following the SCR 11, the cathode potential of the SCR 11 is raised for a short time as a result of the discharge of the capacitor 61 and thereby the SCR 11 is disabled. Therefore, the lamps will be individually illuminated one by one, as in the case of a ring counter operation, and it would be impossible to illuminate a plurality of lamps at the same time. As described above, the circuit including the diodes 72 and 73 serves the function of illuminating a plurality of lamps at the same time and also serves the function of concurrently turning off the all lamps.

Referring next to FIG. 2 representing a first modification of the circuit of FIG. 1, except single-pole double-throw switches 6 and 7 are respectively inserted between the SCR 11 and the resistor 52 and between the SCR 12 and the resistor 53. In the both switches, the movable contact is connected to the resistor and two fixed contacts are respectively connected to the anode and cathode electrodes of the SCR. The movable contacts of the both switches are preferably interlocked.

When the movable contacts of the switches 6 and 7 are connected to the cathodes of the SCR’s 11 and 12, the circuit operation is identical to that of the circuit of FIG. 1. However, when the movable contacts are switched to the anode side (opposite side in the drawing), this circuit operates as follows.

While none of the SCR’s conducts at first, current flows in the diodes 31, 32, and 33 through the series connection of the resistors 51 and 91, the series connection of the resistors 52 and 92 and the series connection of the resistors 53 and 93, respectively. The first trigger pulse supplied from the trigger pulse generator 3 under these conditions cancels the current

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At this time, the cathode potential of the SCR 13 rises and a current flows in the diode 34 through the resistor 54 and 94. The second trigger pulse then supplied cancels the current in the diode 34 and raises the potential at the junction of the resistor 94 and the diode 34. This potential is transferred through the capacitor 44 to the gate electrode of the SCR 14 and drives it into conduction. Thereby, the cathode potential of the SCR 14 is raised and therefore the commutating capacitors 61,62, and 63 are discharged concurrently to raise the cathode potentials of the SCR’s 11, 12, and 13 for a short time rendering these SCR’s.11, 12, and 13 nonconductive and extinguishing all of the lamps 21, 22, and 23 at the same time.

When the third trigger pulse is supplied, the SCR’s 11, 12 and 13 are again driven into conduction to illuminate the lamps 21, 22, and 23 at the same time, and the commutating capacitor 61 is charged to render the SCR 14 nonconductive.

By repeating the abovementioned operation, the lamps 21, 22 and 23 are concurrently and cyclicly illuminated and extinguished. It is noted that the group of three SCR’s 11,12, and 13 and the SCR 14 cooperate to form a circuit similar to a flip-flop circuit. Thus this circuit can be used for indicating emergency parking of the automobile.

The circuit of FIG. 3 is a second modification of the circuit of FIG. 1 and is similar to it, except that the junctions of the resistors 52 and 92 and the resistors S3 and 93 are connected through respective diodes 122 and 123 and a common single-pole single-throw switch 8 to the positive electrode of the d.c. source 1. It will be readily understood that this circuit operates in the same manner as the circuit of FIG. 2 when the switch 8 is closed.

In the above embodiments, if it is assumed that the lamps 21, 22 and 23 are used for indicating a right turn of the automobile, it is necessary to change connections to the lamps 21, 22 and 23 to another set of three lamps (not shown) for a left turn. This can be accomplished by inserting a relay or change-over switch in the cathode side of each SCR.

A further modification of the circuit may include an indicating lamp 130 having a high internal resistance and relatively low power consumption and connected between the anode and cathode electrodes of each of the SCR’s 11, 12, and 13. These indicating lamps may be arranged on the meter panel for the operator in the automobile to confirm the operation of the lamps 21, and 23 and indicate malfunctions relating to the lamps, such as broken filaments, disconnections and improper contacts.

In the above mentioned embodiments, the resistor 24 can be replaced by a lamp which is disposed on the front or side of the automobile, though the time of illumination is short and the time it is extinguished is long.

Since in the circuit of this invention one terminal of each lamp is connected directly to the negative terminal of the source, the circuit can be conveniently installed in automobiles of negative-grounded type.