GB2289450A

GB2289450A - Warning circuit for levelling control systems

Info

Publication number: GB2289450A
Application number: GB9509366A
Authority: GB
Inventors: Frederic Hauck
Original assignee: Delphi Automotive Systems France
Current assignee: Delphi Automotive Systems France
Priority date: 1994-05-18
Filing date: 1995-05-09
Publication date: 1995-11-22
Anticipated expiration: 2015-05-09
Also published as: GB9509366D0; FR2720156B1; GB2289450B; DE19517972A1; FR2720156A1; GB9409929D0; DE19517972C2

Description

i 1 2289450 WARNING CIRCUIT FOR LEVELLING CONTROL SYSTE is The present

invention relates to a warning circuit for a levelling control system used on a motor vehicle.

It is known in motor vehicles to use a levelling system to actively control the levelling of the vehicle. Such a known system generates and uses pressurised air to effect levelling, and includes an air compressor, and an optical sensor to monitor the trim or level state of the vehicle. Further, the pressure of the air in the levelling control system influences the apparent load on the motor vehicle, and the value of the apparent load can be used to control the actuation of a proportioning valve in the braking system of the vehicle.

US-A-4517832 describes a method of diagnosing component failure in a vehicle air suspension system. The method sequences the various components through their intended functional capabilities by selectively energising the components and monitoring them to determine their functional condition. This is a stand-alone system which requires complicated computer control and analysis.

An object of the present invention is to provide a warning to the vehicle operator if a fault occurs in the levelling control system.

To this end, a warning circuit in accordance with the present invention for a levelling control system including an air pressure generating means and an optical sensor, comprises a warning means; switch means which, on actuation, operates the warning means; and monitoring means for providing a signal to the switch means to actuate the switch means, the monitoring means monitoring (1) the status of the air pressure generating means and providing the signal when the air pressure generating means is in an 2 inoperable state, and (2) the status of the optical sensor and providing the signal when the optical sensor is inoperable or the optical sensor indicates that the motor vehicle is out of trim for a predetermined period of time.

In comparison to the system of US-A-4517832, the present invention is less complicated and can simply be added to components already present, and associated with, the levelling control system on the vehicle. No selective energising of the components takes place.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a circuit diagram of a warning circuit in accordance with the present invention for a levelling control system; and Figure 2 is a circuit diagram of an alternative embodiment of a warning circuit in accordance with the present invention.

Referring to Figure 1 of the drawing, the warning circuit 10 comprises a warning lamp 12; switch means 14; and monitoring means 16. The levelling control system for the motor vehicle comprises an optical sensor 18 and an air pressure generating means in the form of an air compressor 20. A fuse 22 is associated with the air compressor 20. The levelling control system acts on or with the suspension system (not shown) of the motor vehicle to actively maintain the vehicle in a substantially level trim relative to the road surface on which the vehicle is travelling. Level trim is attained by generating air pressure with the air compressor 20 and controlling the level of air pressure in a suspension unit (not shown) at the rear of the vehicle. The optical sensor 18 monitors the is 1 1 3 trim of the vehicle and acts to control the operation of the air compressor 20, and hence the trim of the vehicle. A braking system (not shown) of the motor vehicle may also include a proportioning valve which acts to limit the pressure of brake fluid being applied to the rear brakes of the vehicle. Such a proportioning valve can be sensitive to and actuable by the load on the vehicle. The presence of a levelling control system will influence the effective load on the vehicle, and hence the actuation of such a proportioning valve. The present invention aims to provide a warning to the vehicle operator if a fault occurs in the levelling control system.

A power supply (not shown), which is preferably the vehicle battery, provides a first supply voltage V, of typically 12 volts and a second supply voltage V2 of typically 5 volts for the levelling control system and the warning circuit 10. V2 is preferably generated from V, by the circuit 27.

V, is provided after the ignition is switched on. Preferably associated with the warning circuit 10 is a brake fault monitoring system 24 which lights a brake fault warning lamp 26 if a fault is detected in the braking system (not shown) of the motor vehicle.

The switch means 14 comprises a transistor 28. The transistor 28 has its collector connected to the warning lamps 12,26, its base connected to the monitoring means 16 by way of a resistor 29 and to electrical ground 30 by way of a resistor 31, and its emitter connected to electrical ground 30. When the monitoring means 16 detects a fault in the levelling control system (as explained below in greater detail), the monitoring means provides a signal at the base of the transistor 28 to switch the transistor to a conducting state, thereby lighting both warning lamps 4 9 12,26. Associated with the transistor 28 is a circuit which comprises a pair of transistors 32,34, a pair of resistors 33,35, and a capacitor 36. One of the transistors 32 has its collector connected to the collector of transistor 28 by way of resistor 33, its base connected to the base of transistor 28 by way of resistor 35 and resistor 29 and to one side of the capacitor 36, and its emitter connected to the base of the other transistor 34. The other transistor 34 has its collector connected to the base of transistor 28, and its emitter connected to electrical ground 30. The other side of the capacitor 36 is also connected to electrical ground 30. With this arrangement, if a signal is being supplied by the monitoring means 16 to the base of transistor 28 by way of the resistance bridge 29,31, and, one of the warning lamps 12,26 fails and acts as a short circuit between the collector of transistor 28 and supply voltage V,, the circuit acts to prevent the transistor 28 being damaged by excess current flow.

The monitoring means 16 is effectively split into two circuits, one of which monitors the state of the air compressor 20, with the other monitoring the state of the optical sensor 18. Associated with the air compressor 20, the monitoring means 16 comprises a transistor 38 which has its collector connected to supply voltage V2 by way of a resistor 40 and to the base of transistor 28 by way of diode 37 and resistance bridge 29,31, its emitter connected to electrical ground 30, and its base connected to one side of the fuse 22 by way of a resistance bridge comprising a pair of resistors 42,44. During normal operation, a voltage is supplied to the base of the transistor 38 to switch the transistor 38 on, thereby shunting the supply voltage V2 to electrical ground 30. If a fault occurs in the air compressor 20 and the fuse 22 is blown, the transistor 38 is switched off, and the supply voltage V2 supplies the signal to the base of the transistor 28 by way of the diode 37 and resistance bridge 29,31 to light the warning lamps 12,26.

Associated with the optical sensor 18, the monitoring means 16 comprises a timer circuit 46 having an output 48 connected to the base of transistor 28 by way of a diode 39 and resistance bridge 29,31, and an input 50 connected to the optical sensor 18 by way of an amplifying circuit 52. The amplifying circuit 52 comprises a pair of transistors 54, 56. One of the transistors 54 has its base connected to the optical sensor 18 by way of a resistance bridge comprising resistors 58,60. Both transistors 54,56 have their collectors connected to supply voltage V2 by way of resistors 62,64 respectively. Transistor 56 has its base connected to the collector of transistor 54 by way of a resistor 66, and its collector connected to the input 50 of the timer circuit 46. Both transistors 54,56 have their emitter connected to electrical ground 30. A capacitor 68 is connected between the collector of transistor 56 and electrical ground 30. When the optical sensor 18 is operating correctly or is indicating that the levelling control system is operating correctly, the transistor 54 is switched on and the transistor 56 is switched off, as a consequence of which the supply voltage V2 provides a voltage signal of a predetermined level at the input 50. However, if the optical sensor 18 becomes electrically disconnected or if the optical sensor indicates that the levelling control system is not functioning correctly (for example, when the rear of 6 the vehicle is too high or too low for a predetermined period of time set by the timer circuit 46, as described below), the transistor 54 is switched off and the transistor 56 is switched on shunting the supply voltage V2 to electrical ground. As a consequence, no voltage signal is provided at the input 50. Also, if a short circuit occurs in the circuitry of the levelling control system associated with the optical sensor 18, a substantially square wave voltage signal is provided by the optical sensor 18 to the amplifying circuit 52. The amplifying circuit 52 converts this square wave signal to a form of saw-tooth signal which has its voltage peak below the predetermined level at the input 50, which therefore has the same effect as supplying no voltage signal to the input 50.

The timer circuit 46 preferably comprises a counter circuit 70 and a transistor 72. The counter circuit 70 has a number of inputs and outputs which include the input 50 and output 48 for the timer circuit 46. The transistor 72 has its base connected to the output 48 of the timer circuit 46 by way of a resistor 74, its emitter connected to electrical ground 30, and its collector connected to other inputs of the counter circuit 70 by way of two resistors 76,78 and a capacitor 80. The resistors 76,78 and capacitor 80 are used to provide a clock in order to run the timer circuit 46. When a voltage signal above the predetermined level is provided at the input 50, that is, when no fault is monitored by the optical sensor 18, the counter circuit 70 provides no signal at the output 48.

When no voltage signal or a voltage signal below the predetermined level is provided at the input 50, that is, indicating a fault, a signal is provided 1 7 is at the output 48. Without the preferred presence of the transistor 72 and the resistor 74, the counter circuit 70 is such as to provide a substantially square wave signal at the output 48 having a frequency set by the counter circuit for no voltage signal or a voltage signal below the predetermined level at the input 50. This would result in the warning lamps 12,26 flashing on and off when a fault occurs in or associated with the optical sensor 18 of the levelling control system. The frequency set by the counter circuit 70 is the same as the predetermined period of time mentioned above for which the optical sensor 18 monitors the rear of the vehicle being too high or too low. The arrangement of the transistor 72, resistors 74,76,78 and capacitor 80 is such that a signal is fed back to the counter circuit 70 which modifies the signal at the output 48 to provide a signal with a steady state level. As a consequence, the warning lamps 12,26 remain permanently lit whilst a fault is detected.

The second embodiment of warning circuit 100 shown in Figure 2 comprises a warning lamp 12; and a first microprocessor 102 which provides both switch means and monitoring means. The levelling control system for the motor vehicle includes a second microprocessor 104 (which incorporates an optical sensor 18) which monitors if the vehicle is level or not, an air compressor 20 and associated fuse 22. The first microprocessor 102 replaces the components shown in Figure 1, but acts in the same way and provides the same outcome. The second microprocessor 104 has a direct connection to the vehicle battery as shown by the prefix BAT in Figure 2. Prefix V, indicates a power supply which is provided after the vehicle ignition is switched on, as in Figure 1. The 8 levelling control system includes an exhaust valve 106 which is actuated by the second microprocessor 104 to reduce the air pressure in the levelling control system. The levelling control system also includes a relay 108 positioned between the air compressor 20 and the fuse 22.

The first microprocessor 102 switches on the warning lamp 12 by connecting line 114 to electrical ground. The first microprocessor 102 is connected to the fuse 22 by way of line 116. Line 116 is connected to line 118 to the relay 108 and to line 120 to the second microprocessor 104. The first microprocessor 102 monitors the operation of the air compressor 20 and the optical sensor 18 by checking the status of the fuse 22 by monitoring the voltage on line 116, and monitors the status of the exhaust valve 106 by checking for a signal on line 107. The first microprocessor 102 also monitors if the vehicle is out of trim, as indicated by the optical sensor 18, by a signal on line 122.

The warning circuit 100 has additional features when compared to the warning circuit 10 of Figure 1. A pressure sensor 110 monitors the level of air pressure in the levelling control system of the vehicle. The pressure sensor 110 provides a signal (voltage V,) to the first microprocessor 102 when the pressure in the levelling control system passes above a predetermined first threshold, and no signal when the pressure falls below a predetermined second threshold. The first threshold is higher than the second threshold. If a signal is received by the first microprocessor 102 from the pressure sensor 110, the first microprocessor 102 turns off the relay 108, by providing a signal on line 124, to turn off the air compressor 20 to prevent unnecessary actuation of the 9 air compressor. Similarly, if the second microprocessor 104 monitors that the vehicle is level, the second microprocessor turns off the relay 108.

However, if no signal is received by the first microprocessor 102 from the pressure sensor 110 and the second microprocessor 104 monitors that the vehicle is not level, the relay 108 is turned on, to turn on the air compressor 20.

As mentioned above, the first microprocessor 102 also receives a signal from the line 107 connecting the second microprocessor 104 to the exhaust valve 106. If the exhaust valve 106 is switched off, the signal received by the first microprocessor 102 is voltage BAT. If the exhaust valve 106 is switched on or has a mechanical fault, the signal received by the first microprocessor 102 is substantially at electrical ground. If the first microprocessor 102 monitors that the exhaust valve 106 is switched on or has a mechanical fault, the first microprocessor switches off a valve 112 associated with a proportioning valve (not shown) of the braking system of the vehicle. If the first microprocessor 102 monitors that the exhaust valve 106 is switched off, the first microprocessor switches on the valve 25 112. The valve 112 controls the operation of the proportioning valve. This arrangement prevents the proportioning valve incorrectly assessing the status of the levelling control system. The present invention therefore provides a visible warning to the vehicle operator should a fault occur on the levelling control system which may affect the handling and braking of the vehicle. Although the preferred embodiment describes the use of a warning lamp 12, this may be replaced by or supplemented with, an audible warning device.

9

Claims

Claims:

1. A warning circuit for a levelling control system including an air pressure generating means and an optical sensor on a motor vehicle, comprising a warning means; switch means which, on actuation, operates the warning means; and monitoring means for providing a signal to the switch means to actuate the switch means, the monitoring means monitoring (1) the status of the air pressure generating means and providing the signal when the air pressure generating means is in an inoperable state, and (2) the status of the optical sensor and providing the signal when the optical sensor is inoperable or the optical sensor indicates that the motor vehicle is out of trim for a predetermined period of time.

2. A warning circuit as claimed in Claim 1, wherein the warning means is a warning lamp.

3. A warning circuit as claimed in Claim 2, in which the motor vehicle includes a warning lamp for indicating a fault in a braking system of the motor vehicle, wherein the switch means, on actuation, also operates the warning lamp for the braking system.

4. A warning circuit as claimed in any one of Claims 1 to 3, wherein the monitoring means comprises a transistor having a collector connected to a supply voltage and to the switch means, a base connectable to a fuse associated with the air pressure generating means, and an emitter connected to electrical ground, the supply voltage providing the signal to the switch means when the fuse is open circuit.

5. A warning circuit as claimed in any one of Claims 1 to 4, wherein the monitoring means comprises a timer circuit having an output connected to the switch means and an input connectable to the f- 11 optical sensor, the timer circuit providing the signal to the switch means when a signal at the input is below a predetermined voltage level.

6. A warning circuit as claimed in Claim 5, wherein the timer circuit comprising a counter circuit and a transistor, the counter circuit providing the input and the output for the timer circuit, and the transistor having a base connected to the output, an emitter connected to electrical ground, and a collector connected to the counter circuit, the transistor adjusting the signal to the switch means when the signal at the input is below the predetermined voltage level.

7. A warning circuit as claimed in any one of Claims 1 to 6, wherein the switch means comprises a transistor having a collector connected to the warning means, a base connected to the monitoring means, and an emitter connected to electrical ground.

8. A warning circuit as claimed in any one of claims 1 to 3, wherein the switch means and the monitoring means are provided by a microprocessor.

9. A warning circuit as claimed in claim 8, wherein the monitoring means monitors the level of air pressure in the levelling control system and provides the signal when the air pressure is below a predetermined level.

10. A warning circuit substantially as hereinbefore described, with reference to, and as shown in, Figure 1 or Figure 2 of the accompanying drawings.