GB2039117A - 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 indicate that an engine parameter has exceeded or fallen below a given value. A number of engine parameters are monitored by devices (M5 to M8) connected in series with respective resistors (R15 to R18) 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). The system also includes a timed operating circuit (C1, R1 to R3) for giving a timed audible indication of other events, e.g. that the vehicle's lights have been left switched on after the engine has been switched off. <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 these operation may not become immediately apparent to the driver, particularly if 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 drive, so that he temporarily looses his concentration.

It is an object of the invention to provide an audible warning system for vehicles which will given an indication to the driver that a fault has developed.

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; a plurality of monitoring devices, each monitoring a different parameter; a plurality of resistors, connected in series with respective monitoring devices; means for connecting said oscillator circuit to a first potential derived through the ignition switch of the vehicle, said monitoring devices completing the circuit to a second potential in parallel, whereby said electro-acoustic transducer emits a pulsed tone when one of said monitoring devices is operated.

Preferably said resistors have different values of resistance whereby the frequency of the pulses emitted by the electro-acoustic transducer will indicate which monitoring device has operated.

In addition to the above, an audible warning may be given to indicate that the vehicle's lights have been left on after the engine has been switched off. Preferably, such an audible warning is provided on a time basis so that the warning only lasts for a given time.

Furthermore, it may be desirable to monitor other non vital parameters such as the level of liquid in the reservoir of the windscreen washers or tyre pressure. An audible warning of low liquid level in the reservoir or low tyre pressure may thus be given when the engine is switched off.

The present invention will now be described in greater detail by way of examples with reference to the accompanying drawings, wherein: Figure 1 is a general circuit diagram of audible warning system for a motor vehicle; Figure 2 is a circuit diagram of one preferred form of audible warning system; Figures 3A and 3B are printed circuit boards showing the arrangement of the circuit components of Fig. 2 on two printed circuit boards; Figures 4A and 4B show one form of housing for the two board embodiment shown in Figs. 1 and 2.

Figures 5A and 5B show an alternative form of housing for the two board embodiment shown in Figs. 2 and 3.

Figure 6 is a circuit diagram of a modified form of audible warning system in which the components are printed on a single board; and Figure 7 is a printed circuit board showing the arrangement of the circuit components of Fig. 6 on a single printed circuit board.

Referring first to Fig. 1, the general circuit comprises an oscillator 0, a speaker Z, and series of monitoring devices M1, M2, and M4 to M8, which are in the form of switches.

In an alternative form, a transducer exhibiting a change in resistance may be used instead of the switches shown.

The oscillator 0 comprises an inductance L1, capacitors C2 to C4, resistors R2 and R3 and a transistor T1, 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 transistor T1 through a diode D9, 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 T1.

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 via the ignition switch S and a diode D3. The oscillator is earthed or connected to the negative terminal of the vehicle's battery through any one of the parallel circuits including the monitoring divices M5 to M8. These four parallel circuits each respectively comprise resistors R15 to R18, diodes D5 to D8 and the monitoring devices M5 to M8. In this example the monitoring devices M5 to M8 respectively relate to brake fluid level (M5); choke (M6), oil pressure (M7) and engine coolant tempera ture (M8). These four monitoring devices are intended to be operational when the engine is running.So long as the switches connected to these four 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 engine coolant temperature exceeds a given temperature, then the switch associated with the monitoring device M8 closes thus earthing the oscillator 0 through the resistor R18, the diode D8 and the closed switch M8. The oscillator 0 is thus rendered operative and emits a pulsed tone whose frequency of pulsation is determined by the value of the resistance of the resistor R18.

By choosing the values of resistance of the resistors R15 to R18 between 0 and 33 ohms, the oscillator 0 will operate at different pulse rates, and audible volumes depending on which resistor R15 to R18 is connected in series therewith. Hence the pulse rate of the tone emitted by the speaker Z will be an indication of which monitoring device M5 to M8 has been operated thus giving an audible indication to the driver, without him having to visually check his instruments or warning lights.

If simultaneous faults occur, the input in series with the lowest resistance will overide the other or others. Hence the audible indication given can represent the major fault, e.g.

loss in oil pressure.

In order to give the driver a warning that his lights have been left on after the ignition has been switched off monitoring devices M1 and M2 monitor the side and head lights respectively. Resistors R 11 and R12 and diodes D1 and D2 respectively constitute the parallel warning circuits associated with the monitoring devices M1 and M2. The common junction between the resistors Ri 1 and R12 is connected to that side of the tank circuit remote from the collector electrode of the transistor Ti. A capacitor C1 is connected across the diode D9, said capacitor constituting a timed operating circuit.A resistor R1 is connected between the junction of the resistors R11 and R12 and the multi-junction between the resistors R15 to R18.

If for example the side lights 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 changes through the closed loop comprising the resistors R2 and R3. The values of the various components involved in the charge circuit are choosen 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 side or side and head lights are still switched on. Again the resistors R11 and Ri 2 have difference values so that the oscillator will output different pulse rates depending on whether only the resistor Ri 1 is in circuit or whether both resistors Ri 1 and R12 are effectively connected in parallel.

Finally, a check on the level of liquid in the reservoir supplying the windscreen washers will be available with the engine switched off.

The monitoring device M4 associated with the reservoir of the washing liquid is connected to the positive terminal of the battery and to the oscillator 0 through a diode D4 and a resistor R14. If the contact of the monitoring device M4 is closed when the engine is off, a continous audible pulsed tone will be emitted by the speaker Z.

Referring now to Figs. 2, 3A and 3B one preferred form of circuit which can be mounted on two printed circuit boards, is basically the same as the circuit shown in Fig.

1 with the exception that there are three timed inputs associated with the monitoring devices M1, M2 and M11 and the washer monitor is omitted. Resistors R15 and R18 are omitted from this circuit, and a resistor R21 and a diode D11 are inserted in series with the monitoring device M11. Also a resistor R4 is inserted in the lead connected to the ignition switch.

Referring specifically to Figs. 3A and 3B the circuit components C1 to C4, R1 to R4, D9, L1 and T1 are printed on a first printed circuit board By, whilst the remaining components with the exception of the monitoring devices and the speaker Z are printed on a second printed circuit board B2. The two boards B1 and B2 are interconnected via leads X1, X2, X3, X4 and X5. The speaker Z is connected across the leads X3 and X4.

External connections Al to A8 are connected to the monitoring devices associated with the vehicle lights, the ignition switch and the other monitoring devices associated with the other parameters.

One preferred form of housing for the two board version shown in Figs. 2 and 3 and spring clip for retaining the housing to the dashboard of the vehicle is shown in Figs. 4A and 4B respectively. The housing comprises two sections H1 and H2 each of frusto-conical shape. The lower section H2 houses the two printed circuit boards B1 and B2, the board B2 being supported over the board B1. The speaker Z is housed within the upper section Hi. Eight spade terminals V are arranged around the junction between the two sections H1 and H2 of the housing. These spade terminals V act as the connecting points to the monitoring devices and the ignition switch of the vehicle.

The spring clip shown in Fig. 4B comprises a base portion U and four equi-spaced resilient arms P which are arranged to grip the sides of the housing, in particular the upper housing Hi. The base portion U is screwed or otherwise fixed to the dashboard of the vehicle and the housing can be pushed into the resilient arms P. The appropriate connecting leads to the monitoring devices M and the ignition switch S are attached to the spade terminals V.

An alternative form of construction of the housing and the spring clip is shown in Figs.

5A and 5B. In this form the two sections H1 and H2 of the housing a cylindrical and the spade terminals V project from the wall of the lower housing H2. The clip is substantially identical with that shown in Fig. 4B, except that the ends of the arms P are turned inwards in order to engage in a groove in the top of the upper housing H1.

In addition to the audible pulse rate tones provided by the speaker Z, a plurality of light emitting diodes may be connected in series with respective resistors associated with the monitoring devices and these would flash in synchronism with the audible output.

A second preferred form of the invention is shown in greater detail with reference to Figs.

6 and 7, in which all the circuit components are mounted on a single printed circuit board.

In this simplified version there is only one timed monitoring associated with the lights of the vehicle and two continuous monitoring devices M5 and M7 associated with brake failure and loss of oil pressure, respectively. In addition a diode D10 replaces the diode D3 in the general circuit of Fig. 1.

The above described audible warning systems have the following advantage.

(a) They can operate satisfactorily over a voltage range of from 8 to 20 volts on the continuous mode and from 8 to 15 volts on the timed mode.

(b) The normal operating current consumption is very small of the order of 1 OmA and falls to 0.25mA on the timed mode, when the capacitor C1 is fully charged.

(c) The choice of the continous and timed pulse mode is useful for differentiating between different types of monitoring, i.e. those which could cause damage to and running engine, and those which could drain a battery when the engine is not running.

(d) By pre-selecting pulse rates and audible volumes it is possible to discriminate between different types of faults or conditions without the driver having to make a visual check.

(e) Loud slow pulse rates overide weaker fast pulse rates, so that the device can automatically discriminate between simultaneous faults and produce a tone indicating the major fault.

(f) The system is housed within a convenient housing and easily fixed to the dashboard of any type of vehicle.

Claims (6)

1. An audible warning system for vehicles for indicating when certain parameters exceed or fall below given limts, said system including: an oscillator circuit; an electro-acoustic transducer connected to said oscillator circuit; a plurality of monitoring devices, each monitoring a different engine parameter; a plurality of resistors, connected in series with the respective 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, whereby said electro-acoustic transducer emits a pulsed tone when one of said monitoring devices is operated.

2. An audible warning system according to claim 1, wherein said plurality of resistors have different values of resistance.

3. An audible warning system according to claim 2, wherein it includes a timed operating circuit operable when the engine is switched off to indicate the state of other parameters associated with the vehicle.

4. An audible warning system according to claim 1 or 2, wherein said continuous monitoring devices monitor any one or more of the following: oil pressure, brakes, choke and engine coolant temperature.

5. An audible warning system according to claim 3, wherein said timed monitoring devices monitor any one of or more of the following: side lights, head lights, level of washer liquid; and tyre pressure.

6. An audible warning system for vehicles for indicating when certain parameters exceed or fall below certain limits, constructed substantially as herein described with reference to and as illustrated in Fig. 1 or Figs. 2, 3A and 3B, or Figs. 6 and 7 of the accompanying drawings.