GB2065349A - An audible warning system for vehicles - Google Patents

Abstract

An audible warning system for a road vehicle in which an oscillator (O) is activated and causes a speaker (Z) to emit a pulsed tone to give a warning. Engine oil pressure is monitored by a device (M5) connected in series with a resistor (R15) between the oscillator (O) and one terminal of the battery. The other side of the oscillator is connected to the other terminal of the battery through the ignition switch (S). A timed operating circuit (C1, R1 to R3) for giving a timed audible indication that the vehicle's lights have been left switched on after the engine had been switched off is provided with means (Da, Dc, R'1, R4, R7 and T3) for inhibiting operation if the lights are switched on when the ignition switch is off. Operation of the alarm is also inhibited for a given period after ignition switch is turned on by means (T2, Z1, R8, R9, C5 and Db) in order to allow the engine to be cranked and the oil pressure to have built up to close the switch (M5). <IMAGE>

Description

SPECIFICATION Audible warning system for vehicles The present invention relates to a warning system for vehicles for giving an audible warning when certain engine parameters exceed or fall below given safe limits.

Warning systems for road vehicles are well known, and the standard motor vehicle has warning lights for indicating low oil pressure or battery not charging. More expensive cars may also be fitted with other visual warning lights to indicate loss of brake fluid, hand brake on, choke out, excessive engine coolant temperature.

Warning devices of the audible type are also well known for indicating an open door or a seat belt not fastened.

Warning lights have the disadvantage that their operation may not become immediately apparent to the driver, particularly if used in brilliant sunshine. On the other hand some audible devices fitted to road vehicles manufactured in the United States have the disadvantage that the noise they emit is not only unpleasant, but may unduly startle the driver, so that he temporarily looses his concentration.

Various examples of an audible warning system for vehicles are disclosed in our British Patent Application No. 79.31312 (published under Serial No. 2,039,11 7) which are designed to overcome the above referred to disadvantages, and which will give an indication to the driver that a fault has developed.

One preferred embodiment relating to the detection of brake failure and loss of oil pressure is shown in Fig. 6 of our Patent Application No. 79.31312. This embodiment also contains a provision for giving an alarm, if the vehicle's lights are still switched on after a lapse of 1 5 seconds from the time when the engine was switched off. Also with the engine stationary, operation of the ignition switch before cranking the engine results in an alarm being continuously given until the engine is started and the oil pressure is built up suffici ently to open the oil pressure switch.

As a result of recent trails of the audible warning system shown in Fig. 6 of our British Patent Application No. 79.31312, certain modifications to the circuit are desirable in order to meet specific customer requirements.

The requirements are as follows:- (a) On switching the vehicle's lights on when the engine is not running, no alarm should be given.

(b) On switching the ignition off, there should be a short delay (approximately 2 seconds) to allow the driver to switch his lights off, before the alarm is sounded.

(c) With the engine stationary, operation of the ignition switch before the engine is cranked, should not result in the immediate operation of the alarm. Thus it is required to inhibit the operation of the alarm for a few seconds to enable the engine to be cranked and the oil pressure to have built up sufficiently to close the oil pressure switch.

It is therefore an object of the present invention to provide an audible warning system for vehicles which well meet at least the first of the above three requirements.

According to the present invention there is provided, an audible warning system for vehicles for indicating when certain parameters exceed or fall below given limits, said system including: an oscillator circuit; an electroacoustic transducer connected to said oscillator circuit; n monitoring devices n being a positive integer greater than 1, each monitoring a different engine parameter; at least n - 1 resistors, connected in series with n - 1 of the monitoring devices; means for connecting said oscillator circuit to a first potential through the ignition switch of the vehicle, said monitoring devices completing the circuit to a second potential in parallel, to enable said electro-acoustic transducer to emit a pulsed tone when one of said monitoring devices is operated; a timed operating circuit operable when the engine is switched off to indicate that the vehicle's lights have been left on; and means for inhibiting the operation of said timed operation circuit where the vehicle's lights are switched on intentionally whilst the engine is stationary.

Preferably said timed operating circuit will operate for a given period after the engine has been switched off to indicate that the lights have been left on.

Preferably means are additionally provided for inhibiting the operation of said electroacoustic transducer for a first predetermined time at the commencement of said given period in order to allow the driver to switch off the lights after he has switched off the engine.

Preferably means are provided for inhibiting the operation of said electro-acoustic transducer for a second predetermined time after operation of the ignition switch before cranking the engine.

The present invention will now be described in greater detail by way of example with reference to the accompanying drawings, wherein Figure 1 is a circuit diagram of one preferred form of an audible warning system for a vehicle which will meet both the above two referred to requirements; and Figure 2 is a circuit diagram of an alternative form of audible warning system.

Referring to Fig. 1, the circuit comprises an oscillator 0, a speaker Z, and three monitoring devices M1, M5 and M7 which are in the form of switches, or transducers exhibiting a change in resistance.

The oscillator 0 comprises an inductance L1, capacitors C2 to C4, resistors R2, R3 and R6 and a transistor Tl. The tank circuit of the oscillator is formed by the inductance L1 in parallel with a series circuit comprising the capacitors C3 and C4. One end of this tank circuit is connected to the collector electrode of the transistor T1, whilst the other end is connected to the base electrode of the transistors T1 through a capacitor C1. and a parallel circuit consisting of the resistor R2 and the capacitor C2. The junction between the series capacitors C3 and C4 of the tank circuit is connected to the emitter electrode of the transistor Tl, through the resistor R6.

The speaker Z and the resistor R3 are connected in series between the emitter and base electrodes of the transistor T1. A positive potential is applied to the oscillator 0 via the ignition switch S and a diode D10. The oscillator is earthed or connected to the negative terminal of the vehicle's battery through either one of the parallel circuits including the monitoring devices M5 and M7. The first parallel circuit comprises a resistor R15 a diode D5 and the switch M5. The second circuit comprises a diode D7 and the switch M7. In this example the monitoring device M5 relates to brake fluid level and the monitoring device M7 relates to oil pressure. These two monitoring devices are intended to be operational when the engine is running.So long as the switches connected to these two monitoring devices are open, there is no earth or negative connection to the oscillator 0, hence the oscillator is inoperative and no audible tone is emitted from the speaker Z. If for example the oil pressure falls below a given limit, then the switch M7 associated with the monitoring device closed thus earthing the oscillator 0 through the diode D7, and the closed switch M7. The oscillator 0 is thus rendered operative and emits a pulsed tone whose frequency of pulsation is determined by the value of the resistance in series, in this case zero as the connection is direct. By including the resistor R1 5 in series with the switch M5, the oscillator 0 will operate at two different pulse rates, and audible volumes depending on whether the circuit is completed through the switch M5 or M7.Hence the pulse rate of the tone emitted by the speaker Z will be an indication of which if the two monitoring devices M5 and M7 has been operated thus giving an audible indication to the driver, without him having to visually check his instruments or warning lights.

In order to give the driver a warning that his lights have been left on after the ignition has been switched off, the monitoring device M1 monitors both the side and head lights.

The switch M1 is connected to the oscillator O and the capacitor C1 through a diode D1.

The capacitor C1 is connected in parallel with a diode. D9, said capacitor constituting a timed operation circuit.

If for example the lights of the vehicle are left on after the engine has been switched off, positive potential will still continue to be supplied to the base electrode of the transistor T1 via the capacitor C1. It will be appreciated that there will always be an earth connection through the monitoring device M7 when the engine is switched off. However, the potential at the junction between the capacitor C1 and the parallel circuit comprising the capacitor C2 and the resistor R2. gradually falls as the capacitor C1 discharges through the closed loop comprising the resistors R2 and R3. The values of the various components involved in the charge circuit are chosen such that the oscillator 0 will remain operative for about 1 5 seconds.Thus the driver will be given a limited warning after he has switched his engine off that his lights are still switched on.

In order to meet the first of the above three referred to requirements, the circuit additionally includes diodes Da and Dc, resistors R'1, R4 and R7 and a transistors T3, resistors R'1 and R4 effectively replacing resistor R1 in the circuit of Fig. 6 if our British Patent Application No. 79.31312. The cathode of the diode Da is connected between the junction between the resistors R'1 and R4, whilst the anode is connected to the junction between the diode D5 and the switch M5. The brake fluid level warning lamp X1 is connected between this latter junction and the positive terminal of the battery.The transistor T3 has its emitter electrode connected to the junction between the capacitor C1 and the resistor R2, its collector electrode connected to the junction between the diode D1 and the switch M1 through the resistor R7 and the diode Dc, and its base electrode connected to the anode of the diode D7 through the resistor.

Under normal operating conditions, the switch M5 indicating brake fluid level, is open regardless of whether the ignition switch S is closed or open. The diode Da is effectively connected to the positive terminal of the battery via the brake fluid level warning lamp X1.

A positive voltage is fed through the lamp Xl, the diode Da and the resistor R'1 to charge the capacitor C1 to the full battery voltage when the engine is not running, the switch M7 being closed. The circuit which comprises the transistor T3, the resistors R5 and R7 and the diode Dc enable the capacitor C1 to be rapidly charged when the switch M1 is open and the switch M7 is closed, i.e. when the engine is stationary with its lights switched off. The effect of this rapid charging of the capacitor C1, is that if the vehicle's lights are switched on, the closing of the switch M1 prior to the ignition switch S being closed, will not cause the initiation of the alarm circuit, because current is prevented from passing into the base electrode of the transistor T1 which thus remains non-conductive.

It should be noted that the passage of current through the brake fluid level warning lamp X1 to charge the capacitor, is well below the level to cause the lamp to glow.

In order to meet the third of the above three requirements, the circuit additionally includes a transistor T2, a zener diode Z1, resistors R8 and R9, a capacitor C5 and a diode Db. The base electrode of the transistor T2 is connected to the junction between the diode D1 and the capacitor C1 through a series circuit comprising the resistor R9, a parallel circuit consisting of resistor R8 and the capacitor C5, and the zener diode Z1. The emitter electrode of the transistor T2 is connected to the anode of the diode D7, whilst the collector electrode is connected to the junction between the resistors R2 and R3.

The diode Db is effectively connected across the series circuit comprising the resistor R3 and the parallel combination of the resistor R2 and capacitor C2 for the purpose of reducing the discharge time of the capacitor C1.

When the ignition switch S is closed, a positive voltage is applied via the diode D10 to the lower plate of the capacitor C1 thus raising its potential by approximately 1 2 volts.

As the capacitor is already charged to approximately the same value through the diode Da and the resistor R'1, its upper plate potential will be raised to approximately twice the battery terminal voltage. The zener diode Z1 which has a zener voltage of about 1 6 volts will conduct the excess positive potential to the base electrode of the transistor T2 through the parallel circuit of the resistor R8 and the capacitor C5 and the resistor R9. The transistor T2 is thus rendered fully conductive which renders the transistor T1 non-conductive.The charge on the capacitor C1 will fall exponentially at a rate determined by the values of resistance of the resistors R8 and R9 until it reaches 1 6 volts at which the zener diode cuts off the flow of current to the base electrode of the transistor T2 to allow the transistors T1 to become conductive again, and oscillations to commence.

The purpose of the capacitor C5 is to overcome the initial transient conditions created by the capacitor C2. The diode Db is provided to reduce the discharge time of the capacitor Cl. The resistor R6, which is optional, is for the purpose of increasing the audible volume of the unit and may be a preset variable resistance in order that a desired volume may be preset.

A warning lamp X2 located on the dashboard of the vehicle is provided in conventional manner to indicate that the lights of the vehicle are "on".

In practice the values of the various components are chosen such that the oscillator 0 is inhibited for about 7 seconds, which allows the engine to be started without the alarm being triggered.

To summarize the operation of the above circuits, the following should be noted: (a) The circuit comprising the transistor T2, the zener diode Z1, the resistors R8 and R9 and the capacitor C5 prevents oscillation when cranking.

(b) The circuit comprising the resistor R'1, and the diode Da prevents oscillation when switching the lights on with the ignition off.

(c) The circuit comprising the transistor T3, the diode Dc and the resistors R5 and R7 facilitates rapid charging of the capacitor C1, if the unit alarms due to the lights being left on when the engine is switched off. Momentarily switching the lights off allows this circuit to charge up the capacitor C1 and prevents oscillations when the lights are switched on again.

Additional monitoring devices may be connected in parallel with the switch M5, each having a resistor and diode in series therewith, the resistors having different values of resistance from one another and from the resistor R15.

In an alternative from the anode of the diode Da may be connected to an auxiliary positive voltage supply instead of being supplied through the lamp X1. This modification is desirable if no positive is available at the brake switch when the ignition is off.

Referring now to the alternative circuit shown in Fig. 2, which is designed to meet the second of the three requirements, the circuit is divided into three sections as follows: Section A: Excess voltage protection circuit Section B: Timer/trigger/accept circuit Section C: Oscillator circuit.

The oscillator circuit comprises transistors T21 and T22, resistors R21 to R25, capacitors C21 to C23 and a diode D21. A speaker Z is also included with the oscillator circuit and is in series with the emitter collector path of the transistor T21. The circuit receives a voltage V's from terminal 3 of a timer integrated circuit T in Section B.

The emitter-collector path of the transistor T22 is connected between the base electrode of the transistor T21 and the negative rail.

The diode D21 is connected across the speaker Z.

The resistor R24 is connected between the V's supply rail and the base electrode of the transistor T22, and a junction point X. Connected between the junction point X and the collector electrode of the transistor T2 1 is a series circuit comprising the resistor R25 and the capacitor G23. Connected between the junction point X and the negative rail are two capacitance-resistance networks; the first comprises the resistor R23 and the capacitor C22 connected in series; and the second comprising a parallel circuit consisting of the capacitor C21 and the resistor R21 in series with the resistor R22.

The timer/trigger/accept circuit comprises a transistor T23, resistors R26 to R30, R34 and R35, capacitors C24 to C27, a diode D22 and the timer T. the timer integrated circuit is fo known construction and has eight terminals numbered 1 to 8 which are connected as follows:- Terminal 1: to the negative rail, Terminal 2: to the emitter electrode of the transistor T23 though the capacitor C24 Terminal 3: To the emitter electrode of the transistor T21 to supply the voltage V's to the oscillator circuit C.

Terminal 4: to the negative rail through the capacitor C27.

Terminal 5: to the negative rail through the capacitor C25.

Terminal 6: to the positive rail through the resistor R30.

Terminal 7: to the negative rail through the capacitor C26 and also to terminal 6.

Terminal 8: to the positive rail.

The positive rail is connected to a terminal 12 and thence to the positive pole of the battery through the lights switch. The negative rail is connected to a terminal 13 and thence to the negative pole of the battery through elements in Section C. A terminal Il is connected to the positive pole of the battery through the ignition switch of the vehicle.

Resistors R35 and R36 form a potentiometer chain across the positive and negative supply rails the junction of which is connected to terminal 4 of the timer T. A second potentiometer chain across the supply rails comprises the diode D22 and the resistors R28 and R29. The junction between the resistors is connected to the emitter electrode of the transistor T3. The base electrode of the transistor T23 is connected to the negative rail through the resistor R27 and the collector electrode is directly connected to the negative rail. The resistor R26 is connected between the base electrode of the transistor T23 and the terminal Il through a diode D24 located in Section A.

The excess voltage protection circuit comprises transistors T24 and T25, resistors R31-R33, diodes D23 and D24 and a zener diode Z21. The transistors T25 has its emitter-collector path located in the negative rail.

The diode D23 is connected between the emitter electrode and the terminal 13 and is provided to protect the whole circuit against reverse battery connection. The resistors R32 and R33 from a potentiometer chain across the supply rails. The junction between these two resistors is connected firstly to the base electrode of the transistor T25 and secondly to the collector electrode of the transistor T24.

The base electrode of the transistor T24 is connected to the positive supply rail through the resistor R31 and zener diode Z21 in series. The emitter electrode of the transistor T24 is connected to the negative supply rail.

The excess voltage protection circuit is arranged so that when normal voltage prevails on the positive supply rail the transistor T24 is non-conductive and the transistor T25 is fully conductive. The zener diode Z21 acts as a reference voltage to hold the transistor T24 non-conductive under normal operating conditions. If now an excess voltage is applied to the terminal 12, the zener diode Z21 will conduct this excess voltage which will raise the bias potential applied to the base electrode of the transistor T24. The transistor T24 is thus rendered fully conductive which shortcircuits the resistor R33 and thus lowers the bias voltage applied to the base electrode of the transistor T25 to substantially zero poten tial.This renders the transistor T25 fully nonconductive which thus effectively open-circuits the whole circuit thus preventing damage to the components due to excessive current flow.

The 1 5 second timing period of the timer integrated circuit T is determined by the resistor R30 and the capacitor C26. The timer T is triggered by a negative-going signal which is fed to the terminal 2 via the capacitor C24 when the ignition switch has been turned off to stop the engine. The transistor T23 is normally held conductive whilst the ignition switch is "on". When the ignition switch is opened, the voltage across the resistors R6 and R7 drops substantially to zero so that the base electrode of the transistor T23 is biased to cause the transistor T23 to conduct and thus short-circuit the resistor R29. This results in a negative going pulse being applied to the terminal 2 of the timer T.When the timer T is triggered, the voltage at the terminal 3 rises to V's which is only slightly lower than the value Vs, thus supplying power to the oscillator circuit C. The timer then starts to run for the 1 5 second period until the capacitor C26 has been charged up to the threshold at which the timer T is stopped.

As soon as the timer T is started the voltage V's is applied to the oscillator circuit C, but the latter does not immediately operate to energize the speaker Z until after a 2 second delay determined by the capacitor C21 and the resistors R21 and R22. Thus the oscillator circuit is held inoperative for a 2 second period which allows the driver time to switch his lights off after having switched the ignition off without sounding the alarm.

If the driver switches his lights off after the alarm has sounded but before the expiry of the 1 5 second period, the timer T is rendered inoperative by the potential at terminal 4 falling to substantially zero.

In this embodiment, in order to minimize the current drawn from the battery, the positive supply rail is connected to the battery through the light switch instead of through the ignition switch as in the first embodiment.

Thus, when the lights of the vehicle and the ignition are switched off, the circuit draws no current from the battery, and negligible current when only the ignition is switched on, since except for the voltage across the resistors R26 and R27, none of the rest of the components in the sections A, B and C receives any current.

One effect of this arrangement is that when the lights of the vehicle are switched on with the ignition switched off, the trigger is liable to be energised. This is prevented from happening by the provision of the resistors R34 and R35 together with the capacitor C27.

When the lights are switched on due to the fact that the capacitor C27 has previously discharged through the resistor R34, the terminal 4 is held at the potential of the negative rail for a sufficient time to enable the timer integrated circuit to stabilize thus preventing unwanted triggering of the alarm.

Thus, the operation of the second embodiment is such that the alarm will only be sounded when the lights of the vehicle and the ignition are switched off in a specific sequence, i.e. after 2 seconds from the time that the ignition is switched off with the vehicle lights still on. The alarm will cease after the 1 5 second period should the driver decide to leave his lights switched on.

Claims (7)

1. An audible warning system for vehicles for indicating when certain parameters exceed or fall below given limits, said system including: an oscillator circuit; an electro-acoustic transducer connected to said oscillator circuit; n monitoring devices, n being a positive integer greater than 1, each monitoring a different engine parameter; at least n - 1 resistors, connected in series with n - 1 of the monitoring devices; means for connecting said oscillator circuit to a first potential through the ignition switch of the vehicle, said monitoring devices completing the circuit to a second potential in parallel, to enable said electroacoustic transducer to emit a pulsed tone when one of said monitoring devices is operated; a timed operating circuit operable when the engine is switched off to indicate that the vehicle's lights have been left on; and means for inhibiting the operation of said timed operating circuit where the vehicle's lights are switched on intentionally whilst the engine is stationary.

2. An audible warning system according to Claim 1, wherein said timed operating circuit will operate for a given period after the engine has been switched off to indicate that the lights have been left on.

3. An audible warning system according to Claim 2, wherein means are additionally provided for inhibiting the operation of said electro-acoustic transducer for a first predetermined time at the commencement of said given period in order to allow time for the lights to be switched off after the engine has been switched off.

4. An audible warning system according to any one of the preceding claims, wherein means are additionally provided for inhibiting the operation of said electro-acoustic transducer for a second predetermined time after operation of the ignition switch before cranking the engine.

5. An audible warning system according to Claim 3, wherein said given period is approximately 1 5 seconds and said first predetermined time is approximately 2 seconds after the commencement of the given period.

6. An audible warning system according to any one of the preceding claims, wherein said n - 1 resistors each have a different value of resistance.

7. An audible warning system constructed substantially as herein described with reference to and as illustrated in Fig. 1 or Fig. 2 of the accompanying drawings.