Brake Malfunction Warning and Indicating System for Automobiles

1. Field of the Invention

The present invention relates to a brake malfunction warning and indicating system for use with an automotive brake system.

2. Description of the Prior Art

In the last decade, the number of automobile vehicles has increased quite steadily so that the roads have highly dense traffic. As a result, the casualties due to traffic accidents have also increased accordingly. This requires that automotive vehicles be equipped with double or triple safeguards. As to the brake system, for example, most of the present automotive vehicles adopt a dual brake system. Thus, even when one brake system becomes inoperative by some cause, the other system will perform the braking action, thereby to prevent a traffic accident resulting from the brake malfunction which might otherwise be encountered. Even in this instance, however, the dual system brake will experience the so-called "unbalanced braking phenomenon" when one brake system becomes inoperative. When an unbalanced braking force is imparted to an automotive vehicle running at a high speed, the vehicle can often be subjected to a traffic accident. This unbalance will not, however, occur when the vehicle is running at a normal cruising speed.

It is, therefore, an object of the present invention to provide a brake malfunction warning and indicating system which is capable of detecting and indicating a brake malfunction when at least one brake system of the dual system brake gets out of order.

Another object of the present invention is to provide a brake malfunction warning and indicating system which is capable of memorizing a possible malfunction of a hydraulic circuit of the dual system brake, even when it is deenergized, and indicating the malfunction simultaneously upon its energization.

A further object of the present invention is to provide a highly reliable brake malfunction warning and indicating system including a simplified and inexpensive electronic circuit which is operative to self-maintain a command signal for indication of the brake malfunction.

According to the present invention, there is provided a brake malfunction warning and indicating system for use with a brake system of an automotive vehicle, comprising a stop switch rendered conductive in response to depression of a brake pedal; a brake warning switch normally conductive when the brake pedal is released, and rendered nonconductive when the brake pedal is depressed and the pressure of the working fluid in the brake system is at a normal level, said brake warning switch being rendered conductive in response to a possible malfunction of the brake system in terms of the working fluid when the brake pedal is depressed; a self-maintaining circuit connected between the anode of a power source and said brake warning switch and including switching means which is operative when said stop switch and said brake warning switch are rendered conductive and kept operative till said brake warning switch is rendered nonconductive; and a brake malfunction indicating lamp connected to said self-maintaining circuit and adapted to be energized upon the operation of said switching means of the self-maintaining circuit.

Other objects and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a connecting diagram showing a brake malfunction warning and indicating system according to the present invention;

FIG. 2 is similar to FIG. 1 but shows another embodiment of the present invention;

FIG. 3 is also similar to FIG. 1 but shows a further embodiment of the present invention; and

FIG. 4 is also similar to FIG. 1 but shows a further embodiment of the present invention.

One mode of a brake malfunction warning and indicating system according to the present invention will be described with reference to FIGS. 1 and 2. Reference letter B indicates a power source such as a battery mounted on an automotive vehicle. Letters SW.sub.1 and SW.sub.2 respectively indicate a two-way stop switch rendered conductive by the mechanical displacement of a brake pedal of the automotive vehicle, and a two-way brake warning switch which is always conductive when the brake pedal is released and which is rendered nonconductive when the brake pedal is depressed and the oil pressure in the hydraulic circuit in the brake system is at a normal level. The brake warning switch SW.sub.2 is maintained conductive when the oil pressure is at an abnormal level even with the brake pedal being depressed. Letters SW.sub.3, SW.sub.4 and SW.sub.5 respectively indicate an ignition switch, a starter switch and a parking switch. Letters L.sub.1, L.sub.2 and L.sub.3 respectively indicate a stop lamp, a brake malfunction indicating lamp and a parking lamp. Generally indicated at reference numeral 1 is a self-maintaining circuit which includes a controlled rectifying element Q such as a silicon controlled rectifier (which will be shortly referred to as SCR), a gate bias resistor R.sub.1 and a resistor R.sub.2 for supplying a maintaining current to the SCR. All of these elements are common to the two embodiments of FIGS. 1 and 2. As shown in FIG. 1, on the other hand, reference numeral 2 indicates a check circuit which includes a transistor Tr.sub.1, a base bias resistor R.sub.3 and a diode D.sub.1. In the embodiment of FIG. 2, however, the check circuit 2 includes two diodes D.sub.2 and D.sub.3.

The operations of the two embodiments will now be described with reference to FIGS. 1 and 2.

In the embodiment of FIG. 1, when the ignition switch SW.sub.3 and the starter switch SW.sub.4 are closed to start an engine of the automotive vehicle under discussion, then a base current is supplied to the base of the transistor Tr.sub.1 of the check circuit 2 through the resistor R.sub.3, so that the transistor Tr.sub.1 is rendered conductive. As a result, a circuit composed of the power source B, the ignition switch SW.sub.3, the brake malfunction indicating lamp L.sub.2, the collector and emitter of the transistor Tr.sub.1 and the ground is made to light the brake malfunction indicating lamp L.sub.2. At the same time, another circuit composed of the power source B, the starter switch SW.sub.4, the diode D.sub.1, the parking lamp L.sub.3 and the ground is also made to light the parking lamp L.sub.3.

In the embodiment of FIG. 2, on the other hand, while the starter switch SW.sub.4 is kept conductive, a circuit composed of the power source B, the diodes D.sub.2 and D.sub.3, the brake malfunction indicating lamp L.sub.2 and the parking lamp L.sub.3 is made to light the two lamps L.sub.2 and L.sub.3. These lamps L.sub.2 and L.sub.3 are turned off when the engine is started to render the starter switch SW.sub.4 nonconductive. This implies that it is possible to check the existence of disconnection of the brake malfunction indicating lamp L.sub.2 and the parking lamp L.sub.3 during the starting operation in which the starter switch SW.sub.4 is condictive.

In both of the embodiments of FIGS. 1 and 2, when the parking switch SW.sub.5 is closed with the ignition switch SW.sub.3 being condictive, a circuit including the power source B, the ignition switch SW.sub.3, the parking switch SW.sub.5, the parking lamp L.sub.3 and the ground is made to turn on the parking lamp L.sub.3.

Now, description will follow on the operation of the present brake malfunction warning and indicating system in the case where the brake pedal is depressed to closed the stop switch SW.sub.1 when the vehicle is running.

If it is assumed that the braking oil pressure is at a normal level, the brake warning switch SW.sub.2 is rendered nonconductive when the brake pedal is depressed. Even if, in this instance, an electric current is supplied to the gate of the SCR of the self-maintaining circuit 2 via the stop switch SW.sub.1 and the resistor R.sub.1, the cathode of the SCR is electrically isolated from the ground in the embodiment of FIG. 1 and the anode of the SCR is isolated from the anode of the power source B in the embodiment of FIG. 2. As a result, the SCR is maintained nonconductive to prevent lighting of the brake malfunction indicating lamp L.sub.2. In view of this, the driver can judge that the braking oil pressure is at a normal level. Here, the stop lamp L.sub.1 is turned on by closing the stop switch SW.sub.1.

When, on the contrary, the braking oil pressure is at an abnormal level, then the brake warning switch SW.sub.2 is maintained conductive when the brake pedal is depressed. Since the stop switch SW.sub.1 is also rendered conductive simultaneously, a gate current is supplied to the SCR via the resistor R.sub.1 so that the SCR is rendered conductive. As a result, in the embodiment of FIG. 1, a circuit including the power source B, the ignition switch SW.sub.3, the brake malfunction indicating lamp L.sub.2, the SCR, the brake warning switch SW.sub.2 and the ground is closed to turn on the brake malfunction indicating lamp L.sub.2. In the embodiment of FIG. 2, on the other hand, a circuit including the power source B, the ignition switch SW.sub.3, the brake warning switch SW.sub.2, the SCR, the brake malfunction indicating lamp L.sub.2 and the ground is made to turn on the brake malfunction indicating lamp L.sub.2. Thus, the driver can read the indication that the braking oil pressure is at an abnormal level.

Once the SCR is rendered conductive, it can have its conductivity maintained because a maintaining current is supplied from the power source B to the SCR Q via the resistor R.sub.2 (where the brake warning switch SW.sub.2 is conductive with the brake pedal being released) even if the gate current is blocked out as a result of the nonconductivity of the stop switch SW.sub.1 with the brake pedal being released. While, therefore, the ignition switch SW.sub.3 is kept conductive, the brake malfunction indicating lamp L.sub.2 continues lighting to indicate that the braking oil pressure is at an abnormal level.

When, on the other hand, the ignition switch SW.sub.3 is rendered nonconductive, the brake malfunction indicating lamp L.sub.2 is turned off, but the SCR Q is maintained conductive because the maintaining current is supplied to the SCR Q via the resistor R.sub.2. As a result, when the ignition switch SW.sub.3 is rendered conductive again, the brake malfunction indicating lamp L.sub.2 is turned on at once independently of the conductivity of the stop switch SW.sub.1. Thus, even if another driver takes the place of the foregoing driver, he can recognize at once that the braking oil pressure is at an abnormal level.

After the braking oil pressure again resumes the normal level, the SCR Q will be turned off to extinguish the brake malfunction indicating lamp L.sub.2 when the brake warning switch SW.sub.2 is rendered nonconductive by depressing the brake pedal.

Another mode of the brake malfunction warning and indicating system according to the present invention will now be described with reference to FIG. 3, in which like reference numerals and letters will indicate like elements or parts of FIGS. 1 and 2. In this embodiment, however, the following modifications are made. The reference numeral indicates the self-maintaining circuit which is composed of transistors Tr.sub.2 and Tr.sub.3, resistors R.sub.4 to R.sub.7 and a capacitor C.sub.1. The check circuit 2 is composed of diodes D.sub.4 and D.sub.5. Another reference numeral 3 indicates an indication circuit which is composed of a transistor Tr.sub.4, a resistor R.sub.8 and a capacitor C.sub.2.

The operation of this embodiment will now be described in the following.

When the ignition switch SW.sub.3 and the starter switch SW.sub.4 are turned on to start the engine under consideration, the brake malfunction indicating lamp L.sub.2 and the parking lamp L.sub.3 are also turned on for lighting during the time period while the starter switch SW.sub.4 is kept conductive. This is because the two lamps L.sub.2 and L.sub.3 are supplied with electric energy from the power source B via the starter switch SW.sub.4 and via the diodes D.sub.4 and D.sub.5. The disconnection or breaking of the two lamps L.sub.2 and L.sub.3 can accordingly be checked.

When, on the other hand, the parking switch SW.sub.5 is rendered conductive by application of the side brake while the ignition switch SW.sub.3 is conductive, then an electric energy is supplied from the power source B to the parking lamp L.sub.3 via the ignition switch SW.sub.3 and the parking switch SW.sub.5, so that the parking lamp L.sub.3 is turned on.

Next, an explanation of the operation will be made as to the case where the brake pedal is depressed to close the stop switch SW.sub.1 when the vehicle is running.

Let it be assumed here that the brake pedal is depressed to open the brake warning switch SW.sub.2 when the braking oil pressure is at a normal level. Then, the closing of the stop switch SW.sub.1 will result in providing connection of the stop lamp L.sub.1 with the power source B via the switch SW.sub.1, so that the stop lamp L.sub.1 is turned on.

In the meantime, the transistor Tr.sub.2 has its base connected to and biased by the power source B via the resistors R.sub.4 and R.sub.5, but it has its emitter disconnected from the ground since the brake warning switch SW.sub.2 is non-conductive, so that it is maintained nonconductive. With this transistor Tr.sub.2 being nonconductive, therefore, the base potential of the transistor Tr.sub.4 (or the collector potential of the transistor Tr.sub.2) is elevated to the voltage of the power source B, thus maintaining the nonconductive condition of the transistor Tr.sub.4. As a result, the brake malfunction indicating lamp L.sub.2 is not turned on, which in turn indicates that the brake system is working under a normal condition.

Now, description will follow in the case where the brake warning switch SW.sub.2 is kept conductive even if the brake pedal is depressed, since the braking oil pressure is at an abnormal level. In this instance, the stop lamp L.sub.1 is also turned on in the same manner as has been described above. A base bias having its time constant determined both by the resistor R.sub.4 and the capacitor C.sub.1 is impressed on the transistor Tr.sub.2, when the brake warning switch SW.sub.2 is conductive, so that the transistor Tr.sub.2 is rendered conductive. With this transistor Tr.sub.2 being conductive, the base potential of the transistor Tr.sub.3 (or the collector potential of the transistor Tr.sub.2) is lowered to permit the base current to pass therethrough. As a result, the collector current can pass through the transistor Tr.sub.3, and after that this collector current is supplied to the transistor Tr.sub.2 via the resistor R.sub.5, so that the base potential of the latter transistor Tr.sub.2 will accordingly be elevated. This will be accompanied by an abrupt increase in the collector current of the transistor Tr.sub.2. Once the self-maintaining curcuit 1 receives a trigger signal from the stop switch SW.sub.1 under this condition, it is subjected to such a positive feed-back as it experienced in the Schmidt circuit, so that it is rendered conductive all at once. Once, moreover, the self-maintaining circuit 1 is rendered conductive, it will self-maintain its conductive condition until the brake warning switch SW.sub.2 is rendered nonconductive, even if the stop switch SW.sub.1 is rendered nonconductive. This is because the collector current of the transistor Tr.sub.3 continues flowing into the base of the transistor Tr.sub.2 through the resistor R.sub.5. It should be noted here that since the brake warning switch SW.sub.2 is kept closed when the brake pedal is released, it continues its conductive condition irrespective of the condition of the stop switch SW.sub.1. Therefore, when the self-maintaining circuit 1 is conductive, the base potential of the transistor Tr.sub.4 is lowered so that the transistor Tr.sub.4 is rendered conductive to energize the brake malfunction indicating lamp L.sub.2 for lighting. In view of the lighting lamp L.sub.2, the driver can understand that some trouble exists in the brake system. This lighting will continue until the ignition switch SW.sub.3 is rendered nonconductive.

Even if, however, the ignition switch SW.sub.3 is rendered nonconductive, the self-maintaining circuit 1 can memorize or maintain its conductive condition. As a result, when the ignition switch SW.sub.3 is closed again, the brake malfunction indicating lamp L.sub.2 will be quickly turned on independently of the condition of the stop switch SW.sub.1. Thus, another driver can recognize later that the braking oil pressure is at an abnormal level.

The reason why the time constant circuit composed of the resistor R.sub.4 and the capacitor C.sub.1 is provided in the self-maintaining circuit 1 is that, since the brake warning switch SW.sub.2 is normally closed with the brake pedal being released but it is rendered nonconductive when the brake pedal is so depressed as to have a normal pressure level of the braking oil, there is a time period differential between the instant when the stop switch SW.sub.1 is closed as a result of depression of the brake pedal and the instant when the brake warning switch SW.sub.2 is opened. In other words, without such time delay, the brake malfunction indicating lamp L.sub.2 will be turned on for a short time period even when the braking oil pressure is at a normal level.

The above indicating circuit employs transistors as its constituent elements, but it should be understood that the transistors may be replaced by relays.

Another embodiment of the present invention will be described with reference to FIG. 4, in which like reference numerals and letters will indicate like elements and parts of the afore-mentioned embodiments. In this embodiment, reference letters SW.sub.5 and SW.sub.2 respectively indicate a parking switch, which is manually closed when it is intended to park the automotive vehicle at night, and a pressure switch SW.sub.2 which is provided in the dual systems and adapted to be rendered nonconductive, when the braking oil pressure is at a normal level with the brake pedal being depressed, and rendered nonconductive when the braking oil pressure is at an abnormal level or when the brake pedal is released. Reference numerals L.sub.1 and L.sub.3 respectively indicate a stop lamp and a parking lamp which also acts as a warning lamp which is turned on when the braking oil pressure is at an abnormal level. Reference letters RL.sub.1 and RL.sub.2 respectively indicate first and second relays which have their respective one end connected to the ignition switch SW.sub.3 and to the stop switch SW.sub.1 and their respective other end connected commonly to the pressure switch SW.sub.2. The first and the second relays RL.sub.1 and RL.sub.2 have respectively a normally open contact RL.sub.1a and a normally closed contact RL.sub.2a. Reference numeral RL.sub.3 indicates a latching relay having its movable strip RL.sub.3a moving between the two contacts RL.sub.3b and RL.sub.3c when it is energized. The latching relay RL.sub.3 has its one end connected to the contacts RL.sub.1a and RL.sub.2a of the relays RL.sub.1 and RL.sub.2 and its other end earthed to the ground. Reference letters D.sub.6 and D.sub.7 indicate diodes for preventing backward flow.

The operation of the above circuit will be described in the following.

When the ignition switch SW.sub.3 is closed with the parking switch SW.sub.5 being closed, the warning lamp L.sub.3 is turned on. Then, the driver can inspect whether or not the warning lamp L.sub.3 is in order. Since the stop switch SW.sub.1 is nonconductive under this condition, the first relay RL.sub.1 is kept deenergized. On the contrary, the second relay RL.sub.2 is energized since the pressure switch SW.sub.2 is closed. However, the contact RL.sub.2a of the second relay RL.sub.2 is turned off, and the latching relay RL.sub.3 has its movable strip RL.sub.3a placed in contact with the contact RL.sub.3b, so that the latching relay RL.sub.3 is nonconductive.

Thereafter, the parking switch SW.sub.5 is turned off and the starter switch SW.sub.4 is closed to start the engine running. In this instance, the operation of the case, where the brake pedal is depressed with the ignition switch SW.sub.3 being closed, will be explained in the following.

Since, in this instance, the pressure switch SW.sub.2 is nonconductive when the hydraulic circuit of the brake system is working under a normal condition, the first relay RL.sub.1 is kept deenergized, even when the stop switch SW.sub.1 is closed, and the second relay RL.sub.2 is also kept deenergized. As a result, the latching relay RL.sub.3 is nonconductive so that the warning lamp L.sub.3 is not turned on.

When, on the contrary, a malfunction takes place in the hydraulic circuit in the brake system, the depression of the brake pedal will cause closure of, for example, the pressure switch SW.sub.2. As a result, the first relay RL.sub.1 is energized to close the normally open contact RL.sub.1a, so that the latching relay RL.sub.3 is energized to bring the movable strip RL.sub.3a into contact with the contact RL.sub.3c. This causes simultaneous lighting of the warning lamp L.sub.3. In this way, the driver can recognize that the braking oil pressure is at an abnormal level. Even if the brake pedal is released under this particular condition, the pressure switch SW.sub.2 will maintain its conductive condition, so that an electric current will continue flowing through the first and second relays RL.sub.1 and RL.sub.2. As a result, the normally open contact RL.sub.1a will be closed, whereas the normally closed contact RL.sub.2a will be kept open. With the contact RL.sub.2a being kept open, therefore, the latching relay RL.sub.3 is deenergized to have its movable strip RL.sub.3a in contact with the contact RL.sub.3c, so that the warning lamp L.sub.3 will continue lighting.

Even if the ignition switch SW.sub.3 is closed again, the pressure switch SW.sub.2 will be closed irrespective of the depressed condition of the brake pedal, so that the second relay RL.sub.2 is energized to open the normally closed contact RL.sub.2a. As a result, the latching relay RL.sub.3 is kept deenergized to keep the movable strip RL.sub.3a in contact with the contact RL.sub.3c, so that the warning lamp L.sub.3 is turned on. More specifically, once a malfunction occurs in the hydraulic circuit of the brake system, the warning lamp L.sub.3 can be turned on again when the ignition switch SW.sub.3 is closed again after it has been opened. In this way, the warning lamp L.sub.3 can continue warning that the braking oil pressure is at an abnormal level.

When, on the other hand, the brake pedal is depressed after the malfunction of the hydraulic circuit is repaired to obtain a normal level of the braking oil pressure, the pressure switch SW.sub.2 is rendered nonconductive to block out an electric current to be supplied to the first and the second relays RL.sub.1 and RL.sub.2. As a result, the normally closed contact RL.sub.2a of the second relay RL.sub.2 is closed to allow an electric current to pass through the latching relay RL.sub.3, and the movable contact RL.sub.3a is moved into contact with the contact RL.sub.1a. Since, at this particular instant, the contact RL.sub.1a of the first relay RL.sub.1 is kept open, the latching relay RL.sub.3 will not be energized again. And, the changeover of the contact of the latching relay RL.sub.3 will block out the current supply to the warning lamp L.sub.3.

In the embodiment under discussion, moreover, the opening and closing operation of the pressure switch SW.sub.2 is carried out by the use of the first and the second relays RL.sub.1 and RL.sub.2. However, this operation can be made by alternatively resorting to semi-conductive switching elements such as transistors. This can be accomplished by a transistor which has its collector and emitter connected between the contacts RL.sub.1a and RL.sub.2a of the relays RL.sub.1 and RL.sub.2 and its base connected to the pressure switch SW.sub.2.

Although the above description of the present embodiment has been limited to that where only one of the pressure switches SW.sub.2 detects a malfunction of the brake system, the other or both of the switches SW.sub.2 may likewise perform the same operation for the same purpose.

As has been described hereinbefore, a safer and more reliable brake malfunction warning and indicating system is proposed according to the present invention, which comprises a brake warning switch rendered conductive either when a brake pedal is depressed with the braking oil pressure being at an abnormal level or when the brake pedal is released, a self-maintaining circuit connected to said brake warning switch and rendered conductive, only when said brake warning switch is conductive, for self-maintaining its conductive condition, and an indicating circuit connected to said self-maintaining circuit and rendered conductive, when said self-maintaining circuit is conductive, for turning on a brake malfunction indicating lamp. Thus, it should be appreciated that the indicating lamp will continue lighting, while the braking oil pressure is at an abnormal level, until the pressure is restored to a normal level.