EP0004437B1

EP0004437B1 - Motor vehicle fault indication system

Info

Publication number: EP0004437B1
Application number: EP19790300402
Authority: EP
Inventors: William Frank Hill
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1978-03-18
Filing date: 1979-03-14
Publication date: 1982-01-27
Also published as: EP0004437A1; DE2961938D1; EP0004437B2

Description

This invention relates to a motor vehicle fault indication system including a transducer for detecting a fault and a display device associated therewith.
As the number of fault detecting transducers increases it becomes desirable to associate two transducers with a single display device. In United States Patent 3 302 171 there is shown a system for indicating engine coolant overheating. In this system a single display device is associated with a first transducer for monitoring coolant temperature under normal pressurised conditions and a second transducer for monitoring coolant temperature in the event of pressure loss. If overheating occurs, the display device merely indicates this and it cannot easily be ascertained which transducer has detected the overheating. In the particular case of a system for indicating overheating it is not important for the driver to appreciate which transducer has detected the fault, but in the more general case this is not so.
According to this invention there is provided a motor vehicle fault indication system including first transducer means for detecting a first fault, second transducer means for detecting a second fault, a display device associated with both the first transducer means and the second transducer means, the display device comprising a face marked with a legend and means for illuminating the face, and switch means for selectively rendering the display device responsive to one of said first and second transducer means, the arrangement being such that the display device is normally responsive to said transducer means but, in a predetermined circumstance or in predetermined circumstances, the display device is temporarily responsive to said second transducer means.
As the display device is responsive to the second transducer means only temporarily in predetermined circumstances, the driver can readily appreciate which transducer has detected a fault.
The present invention will now be described in more detail by way of example with reference to the accompanying drawings in which:-

Figure 1 is a circuit diagram of a motor vehicle fault indication system embodying the present invention, and
Figure 2 is a truth table of the operation of the system of Figure 1.

Referring now to Figure 1 there is shown a motor vehicle fault indication system which is installed in a motor vehicle. The motor vehicle includes a conventional internal combustion engine having a spark ignition system, and a water cooling system and associated coolant reservoir. The engine is lubricated by an oil lubrication system which is associated with an oil reservoir. The vehicle also includes a screen washer reservoir for providing a jet of water for washing the windscreen of the vehicle. As will now be described the system is capable of indicating a low level in the coolant reservoir or the screen washer reservoir and is also capable of indicating faults in the oil lubricating system.
The system comprises a battery 10 having its negative terminal connected to earth and its positive terminal connected to an input terminal of an ignition switch I having four operating positing positions la, Ib, Ic, and Id. The position la is an "off" position. In the position ib, the input terminal is connected to a supply line 12 and in the position Ic the input terminal is connected to the supply line 12 and to a supply line 14. The supply line 14 is also connected to the ignition system, and so the position Ic is the normal driving position of the switch. In the position ld, the input terminal is connected to the supply line 14 and also to a relay, not shown, for operating a starter motor. Thus, the position Id is the position for starting the vehicle.
The supply line 12 is connected through two series connected resistors R1, R2 to the supply line 14 and the supply line 14 is connected through a resistor R3 to earth. The junction of the resistor R and R2 is connected to the base of a p-n-p transistor T,, the emitter of which is connected to the supply line 12 and the collector of which is connected through a relay coil B, of a relay B to earth. The supply line 14 is also connected through a push-button switch S and the windings of a motor 16 to earth. The motor 16 drives a pump positioned in the screen washer reservoir. The junction of the switch S and motor 16 is connected to the anode of a diode D,, the cathode of which is connected to the junction of the collector of transistor T, and relay coil B,.
The supply line 12 is connected through a lamp 18 forming part of a display device to an input terminal of a relay switch 8₂ of the relay B. The display device comprises a face marked with a legend depicting a tap to indicate low water level and a means for illuminating the face in the form of the lamp 18. The relay switch B₂ has two output terminals which are connected respectively through two fault detecting transducers in the form of float switches WL and CL to earth. The input terminal is normally connected to the output terminal associated with the float switch CL but, on energization of the relay coil B, is connected instead to the output terminal associated with the float switch WL. The float switch CL is positioned in the engine coolant reservoir and the float switch WL is positioned in the screen washer reservoir. Each float switch closes when the liquid in its respective reservoir falls below a predetermined level.
The line 14 is also connected through two series connected resistors R₄ and R₅ to earth. The junction of the resistors R₄ and R₅ is connected through a resistor R₆ to the junction of the lamp 18 and the input terminal of the switch B₂ and also to the base of an npn transistor T₂. The collector of the transistor T₂ is connected via a resistor R,₃ to the line 12 and the emitter is connected to earth. The collector of transistor T₂ is also connected to the anode of a diode D₂, the cathode of which is connected to the collector of an npn transistor T₃. The collector of transistor T₃ is also connected to the line 14 through a resistor R₇ and the emitter of transistor T₃ is connected to earth.
The line 14 is also connected through a lamp 20 and an oil pressure switch PL to earth. The lamp 20 forms part of a display device, generally similar to the display device associated with the lamp 18 except that its face is marked with a legend depicting an oil can to indicate low oil pressure. The line 14 is also connected through a resistor R₈ and a float switch QL to earth. The float switch QL is positioned in the oil reservoir and closes when the oil falls below a predetermined level. The junction of the resistor R₈ and the float switch QL is connected to the base of the transistor T₃ through a resistor R₉ and the junction of the lamp 20 and the oil pressure switch PL is connected to the base of the transistor T₃ through a resistor R₁₀. The base of transistor T₃ is connected to earth through a resistor R₁₁.
The collector of transistor T₃ is connected to earth through a resistor R₁₂ and also connected to the base of a transistor T₄, the collector of which is connected through a buzzer 22 to the supply line 12 and the emitter of which is connected to earth.
The operation of the fault indication system will now be described with reference to the truth table shown in Figure 2.
If the ignition switch I is in the position la, no fault will be indicated.
If the ignition switch I is moved to the position Ib, the line 12 is energized, the transistor T, is rendered conductive, the relay coil B is energized as indicated by "1" in Figure 2, and the float switch WL is connected in series with the lamp 18. If the float switch WL is open, it will prevent illumination of the lamp 18 but current will be supplied to the base of transistor T₂ thereby rendering this transistor conductive. If the float switch WL is closed, the lamp 18 will be illuminated, thereby providing a visual indication that the water in the screen washer reservoir is below the predetermined level, and the current will be removed from the base of the transistor T₂, thereby rendering it non-conductive, rendering transistor T₄ conductive and energizing the buzzer 22 to provide an audio indication that the water is below the predetermined level. The current supplied to the line 14 through resistors R, and R₂ will be insufficient to illuminate the lamp 20.
With the switch I in the position I_B, the line 14 is at a voltage too low to provide base current to transistors T₂, T₃ and T₄. Hence the buzzer 22 is energized only if the switch W_L is closed enabling base current to flow to transistor T₄ through diode D₂.
Thus, when the ignition switch I is in the position Ib, the condition of the lamp 18 and the buzzer 22 will depend upon the condition of the float switch WL, as indicated by "WL" in Figure 2, and so the level of water in the screen washer reservoir may be checked by moving the ignition switch into this position.
If the switch I is moved into the position Ic, which is the normal driving position, both lines 12 and 14 will be energized thereby rendering the transistor T, non-conductive. With the switch in this position, the float switch CL will normally be connected in series with the lamp 18 with the result that the lamp 18 will be illuminated if the float switch CL is closed, thereby indicating that the water in the coolant reservoir is below the predetermined level. However, if the switch S is depressed to energize the motor 16, relay coil B will be energized and the float switch WL will be connected in series with the lamp 18, which will now only be illuminated if the float switch WL is closed. Thus, with the switch I in the position Ib, the condition of the lamp 18 will depend on the condition of the float switch CL if the switch S is not depressed or upon the condition of the float switch WL is the switch S is depressed. This is indicated in Figure 2 by "CL.S + WL.S".
With the switch I in the position Ic, the lamp 20 will be illuminated if the pressure switch PL is closed, thereby providing a visual indication of low oil pressure. This is indicated in Figure 2 by "PL".
Also with the switch I in the position Ic, the transistor T₂ will be rendered conductive as line 14 is energized and so the condition of the float switch WL and CL will not affect operation of the buzzer 22. If either or both of the switches QL, PL are open, the base of transistor T₃ will receive base current through either or both of the resistors R₈, R₉, thereby rendering the transistor T₃ conductive, the transistor T₄ non-conductive and preventing energization of the buzzer 22. However, if both switches QL, PL are closed, the transistor T₃ will be rendered non-conductive, and the transistor T₄ will be rendered conductive thereby energizing the buzzer 22 to provide an audio indication of low oil pressure combined with low oil level in the oil reservoir. This is indicated in Figure 2 by "PL.QL".
If the ignition switch is moved to the position Id, which is the position for starting the engine, the line 12 will no longer be energized and so the lamp 18 and the buzzer 22 will be inoperative, as is indicated in Figure 2 by "0". However, the condition of lamp 20 will still depend on the condition of the float switch PL.
Thus, the lamp 18 is used to indicate both a low level in the screen washer reservoir and in the engine coolant reservoir, the lamp 18 being normally controlled by the float switch CL, but being controlled by the float switch WL in certain predetermined circumstances, namely when the ignition switch I is in the position Ib, or when the washer switch S is depressed. As the lamp 18 is used for both these purposes it is only necessary to design a single legend.
The fault indication system described above could be extended to include other display devices which are used to indicate two or more faults. For example, this system could include a display device for indicating both a low level in a clutch fluid reservoir and a low level in a brake fluid reservoir, the display device being controlled by a float switch in the brake fluid reservoir when the switch I is in the position Ic and by a float switch in the clutch fluid reservoir when the ignition switch is in the position lb.
It will be appreciated that the circuit shown in Figure 1 makes use of normally open switches WL, CL, QL, PL, which are standard, readily available float-operated and pressure switches. If desired, however, normally closed switches could be specially made for the circuit, but this would involve some circuit modifications.
A further modification which may be thought desirable is an arrangement for preventing continuous operation of the warning devices with the ignition switch in its "auxiliary-only" position. This would involve incorporating a timer to turn off the warning devices after a predetermined time if the ignition contacts of the ignition switch were not closed.

Claims

1. A motor vehicle fault indication system including first transducer means (CL) for detecting a first fault, second transducer means (WL) for detecting a second fault, and a display device (18) associated with both the first transducer means (CL) and the second transducer means (WL), characterised in that the display device (₁8) comprises a face marked with a legend and means for illuminating the face, and in that the system further includes switch means (B) for selectively rendering the display device (18) responsive to one of said first and second transducer means (WL, CL), the arrangement being such that the display device (18) is normally responsive to said first transducer means (CL) but, in a predetermined circumstance or in predetermined circumstances, the display device (18) is temporarily responsive to said second transducer means (WL).

2. A system as claimed in Claim 1 including a driver controlled device (16) associated with a vehicle system in which said second fault may occur, operation of said driver controlled device (16) causing the display device (18) to be rendered responsive to said second transducer means (WL).

3. A system as claimed in Claim 1 or Claim 2 in which the first transducer means (CL) comprises a transducer for detecting the level of fluid in a first reservoir and the second transducer means (WL) comprises a transducer for detecting the level of fluid in a second reservoir.

4. A system as claimed in Claim 3 in which the first reservoir is an engine coolant reservoir and the second reservoir is a screen washer reservoir.

5. A system as claimed in any one of the preceding claims in which the illuminating means comprises a single lamp.