GB2345276A

GB2345276A - Vehicle system malfunction warning method

Info

Publication number: GB2345276A
Application number: GB9828823A
Authority: GB
Inventors: James Henton Wilson; Peter Martin
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1998-12-31
Filing date: 1998-12-31
Publication date: 2000-07-05
Anticipated expiration: 2018-12-31
Also published as: GB9828823D0; GB2345276B

Abstract

A vehicle control system having a plurality of distinct function control systems, such as an electronically controlled braking system, a steer-by-wire system, an electronically controlled suspension system, an electronic engine management system and the like, wherein if a fault is detected in one such function control system, then that function control system and/or one or more other such function control systems is/are arranged to operate with a non-usual behaviour characteristic whereby to bring to the attention of a driver of the vehicle that a fault condition exists in at least one of the function control systems of the vehicle which needs remedial attention.

Description

DESCRIPTION VEHICLE SYSTEM MALFUNCTION WARNING METHOD The present invention is concerned with providing the driver of a vehicle with a warning of the existence in a vehicle system of a malfunction condition.

Recently it has become common to provide motorised road vehicles with complex systems for controlling various aspects of the vehicle's behaviour. For example, many vehicles are now fitted with systems including electronically controlled braking systems, such as electro-hydraulic braking systems (EHB), steer-by-wire, electronic suspension control and engine management systems.

It is common in vehicles having such systems to notify the driver of the existence of a fault using a warning lamp. For instance, a fault such as the failure of a wheel speed sensor, a pressure sensor or a solenoid in an electronically controlled braking system may cause the failure of dynamic braking functions (VSC, TC, ABS) which is indicated by the illumination of a warning lamp. A fault which causes the complete failure of an EHB system and the activation of"push-through"braking is commonly brought to the attention of the driver using another warning lamp, e. g. a red lamp.

A disadvantage of using warning lamps is that they may not be noticed by the driver or they may be noticed but ignored because their significance is not appreciated. The driver may therefore continue to drive as normal, quickly becoming accustomed to the lamp. If the fault is one which causes the disabling of the dynamic braking functions, there will be no change in the "feel"of the brake pedal since EHB remains active so under normal braking conditions the fault will not be detectable by the driver. If a critical fault occurs in the EHB system causing braking to revert to push-through mode which is inferior to EHB, the earliest warning the driver has of the failure, if the warning lamp is ignored or its significance not appreciated, is that the applied braking pressure does not correspond in the usual way to pedal travel.

In accordance with a first aspect of the present invention, there is provided a vehicle having a plurality of distinct function control systems, such as an electronically controlled braking system, a steer-by-wire system, an electronically controlled suspension system, an electronic engine management system and the like, wherein if a fault is detected in one such function control system, then that function control system and/or one or more other such function control systems is/are arranged to operate with a non-usual behaviour characteristic whereby to bring to the attention of a driver of the vehicle that a fault condition exists in at least one of the function control systems of the vehicle which needs remedial attention. If the detected fault is of a non-critical nature, the behaviour of the system which has the fault may be modified.

Alternatively or additionally, the behaviour of other systems may be modified.

The preferred arrangement is that fully functioning systems should be used to produce normally undesirable behaviour to warn the driver there is a serious problem such that he/she is less likely to ignore any warning lamps present.

An example of this is in an electronically controlled braking system which fails and reverts to a hydrostatic backup system. In this mode the performance is very poor. If the system failed at a time when the driver is not braking he/she may not be aware that there is a serious problem until they next use the brakes in which case the performance may not be sufficient. In such a circumstance, a fully functional system can be arranged to produce unpleasant behaviour to warn the driver of a problem. Examples of this can be an engine management system causing rough engine control or a steer-by-wire system shaking the steering wheel. The fully functional systems may decide to give warnings based on fault codes produced by the faulty system and/or lack of communication data from the faulty system.

The amount of unpleasantness produced by the fully functional systems can be scaled according to the severity of the fault and/or the time taken before the driver slows down.

In one arrangement in accordance with the invention, an electronically controlled braking system can be arranged to introduce discomfort to indicate its own faults. However, the discomfort from the brakes can be used for signalling faults from other car systems such as electronically controlled suspension, steer by wire, electric power assist, engine management etc. Also these other systems can be used to create driver discomfort to enhance fault warnings to the driver, e. g. steer by wire could shake the steering wheel when faults are present. Also, where a system has failed into a state where it itself can not introduce driver discomfort, another system can be arranged to cause discomfort and cause the driver to stop or drive carefully. An example of this would be an electronically controlled braking system that fails to its hydrostatic backup. In this state, the braking is poor but traditionally the only warning the driver would have is a red lamp. If the vehicle also has steer by wire it can shake the steering wheel (just the steering wheel, the road wheels would not be affected) so that the driver would be concerned and slow down. In slowing down with the brakes because of the discomfort, the driver would also then be able to feel the poor state of the hydrostatic backup.

In an electronically controlled braking system, such as an electrohydraulic braking system (EHB), there are several levels of operational functionality. There is the normal mode where everything is in its working state. Good base brake, VSC, ABS and TC are available.

Faults may occur such as failed wheel speed sensors that cause the dynamic controls (VSC, ABS, TC) to be disabled, leaving just the base brake functions. This is normally indicated by a yellow fault lamp. However, because for most drivers the dynamic controls are never invoked except in emergencies, they will not notice any performance change. The driver may quickly become used to the presence of the yellow warning lamp, revert to driving as if the system was fully operational and may not bother to get the problem investigated until the next routine service. To counter the driver indifference to the yellow warning lamp, discomfort can be introduced by deliberately making some or all of the brake pressures oscillate. This should not be done where it would risk loss of stability, such as during a hard application, but only when safe to do so, such as normal check braking.

Obviously, a driver could become accustomed to the noise/vibration so the level of discomfort can be increased in relation to the length of time the fault is present. Other physiological strategies such as some random variation in intensity may also be found to be needed.

Another category of faults that puts the yellow lamp on are faults within the base brake hardware of the electronically controlled braking system, such as a failed pressure sensor or failed solenoid. In such cases, the base brake will perform at a lower level of performance than the normal fully functional system. However, it will be better than the backup performance. When these faults are present, the dynamic brake functions will be disabled. With faults in this category, it is important to get the system fixed. So instead of starting with no discomfort and increasing it as time goes on such as in the loss of dynamic brake control case, driver discomfort should preferably be introduced straight away. It could still be increased if the fault does not get attended to.

The final category of faults are ones which cause the system to shut down, turn a red warning lamp on and revert to hydrostatic backup. In such a case, the driver will feel poor performance when he/she brakes. This could cause a problem if the driver needs to brake hard and is unaware that only limited braking is available (he/she may not understand the implications of the red warning lamp). Although the electronically controlled braking system is unable to warn the driver of the problem except by use of the red lamp, it can be arranged to communicate the situation to other systems. For example, the engine management could then limit the vehicle speed, a steer by wire system could shake the steering wheel, etc.

Preferably, the degree of the modification of behaviour varies over time. This variation may be an increase or may be a random or pseudorandom variation. In this way, the driver of the vehicle may be prevented from becoming accustomed to the modified behaviour.

Preferably, the initial degree of modification is dependent on the nature of the fault. A non-critical fault in a system may be indicated by a small modification of behaviour of that or another system. The total failure of a system may, on the other hand, be indicated by a large modification of the behaviour of another system.

According to a second aspect of the present invention, there is provided an electronically controlled vehicle braking system of the type capable of operating in a brake-by-wire mode wherein hydraulic pressure is applied to braking devices at the vehicle wheels in proportion to the driver's braking demand as sensed electronically at a brake pedal, and in a push-through mode wherein hydraulic pressure is applied to the braking devices at the vehicle wheels by way of a master cylinder coupled mechanically to the brake pedal, the electro-hydraulic braking system being operatively connected to one or more other vehicle control system such that when a fault of a prescribed category is detected in the braking system, either said braking system is itself arranged to adopt a modified operational characteristic behaviour, or at least one of said one or more other vehicle control systems is arranged to adopt a modified operational characteristic, the modifications of behaviour characteristic being of such a nature as to be likely to be notable by the driver.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a schematic illustration of a system according to a first aspect of the present invention; Fig. 2 is a schematic illustration of one embodiment of an electrohydraulic braking system to which the present invention is applicable; Fig. 3 is a set of curves of brake pressure (p) against pedal travel (s) showing a number of different pedal behaviours; and Fig. 4 is a pair of graphs showing a) normal braking behaviour and b) braking behaviour modified according to an embodiment of the present invention.

Referring first to Fig. 1, the illustrated system comprises a number of sub-systems, including an electronically controlled braking system 102, a steerby-wire control system 104, an engine management control system 106 and a suspension control system 108 all having data links to a vehicle communications bus 110. Each of the control systems 102,104,106 and 108 feeds to bus 110 a status signal reflecting the status of its respective system.

The nature of the status signal can reflect the condition of the sub-system itself and its component parts. The statuses of the control systems are monitored by a common ECU or each of the control systems 102,104,106,108 also monitors the status of the other systems. In either case, if a fault is detected in one such control system, then that control system and/or one or more others of the control systems is/are arranged to operate a non-usual behaviour characteristic whereby to bring to the attention of a driver of the vehicle that a fault condition exists in at least one of these control systems which needs service attention.

Examples of this are given below.

Fig. 2 shows an example where a fault detected in one control system (an EHB system in this example) is arranged to cause a modified behaviour in the operational characteristic of the EHB control system itself. In Fig. 2, the EHB system comprises a brake pedal 10 with an associated sensor 12 for the acquisition of the driver's braking demand. The driver's demand is transferred to an electronic control unit (ECU1/ECU2) 13, evaluated there, and used as the source for the generation of electrical control signals for proportional solenoid control valves 14a, 14b, 14c, 14d, a hydraulic pump 16, wheel brakes 18a, 18b of one axle supplied with hydraulic fluid by electrically actuated brake channels 20a, 20b and wheels brakes 18c, 18d of the other axle supplied by electrically actuated channels 20c, 20d. Hydraulic fluid for the system is stored in a reservoir 21.

Under normal braking conditions, brake pressure modulation in the electrically actuated brake channels 20a, 20b, 20c, 20d is effected in a known ("brake-by-wire") manner by means of the proportional solenoid control valves 14a, 14b, 14c, 14d, the brake pressure being provided by a pressure accumulator/reservoir 22 whose pressure is maintained by the pump 16 operated by an electric motor 18. The accumulator/reservoir 22 can be selectively isolated by a solenoid operated valve 40.

Pressure sensors 24a and 24b monitor the hydraulic pressure at the wheel brakes 18a, 18b of the front axle and pressure sensors 24c, 24d monitor the hydraulic pressure at the wheel brakes 18c, 18d of rear axle. Further pressure sensors 26,28 monitor the pressure within push-through circuits 27a, 27b for the right and left front wheel brakes and a pressure sensor 30 monitors the supply pressure in the circuit of pump 16. Respective solenoids 29 and 31 enable the brake channels 20a, 20b and 20c, 20d to be coupled together.

The push-through circuits 27a, 27b include respective solenoid controlled valves 32a, 32b to enable these circuits to be closed (open-circuited) during normal brake-by-wire operation.

The push-through arrangement includes a master-cylinder 34 coupled to the brake pedal 10 and to the circuits 27a, 27b, the master cylinder enabling the front brakes to be actuated manually in the event of failure of the brake-bywire system. Coupled to the circuit 27b via a solenoid operated valve 36 is a travel simulator 38 which is activated hydraulically by master-cylinder pressure to give"feel"to the driver during operation of the brakes in brake-by-wire mode. The connection between the master cylinder 34 and the travel simulator 38 is controllable by the electrically operated valve 36, so that unnecessary pedal travel can be avoided during manual actuation by closure of this valve.

The EHB system described this far is already known. In operation, the system is controlled by means of the electronic control units ECU1 and ECU2 which are in communication via a CAN bus. The travel s and/or force F resulting from an actuation of the brake pedal 10 is/are sensed by the sensor means 12.

Furthermore, the brake pressure p which, on an actuation of the brake pedal, is generated in the master cylinder 34, is sensed by the sensor means 26.28. In the EHB braking mode, that is when there is no safety-critical fault condition in the system, valves 32a, 32b are closed and the valve 36 is opened so that, on an actuation of the brake pedal 10, the pedal simulator 38 is actuated for giving the driver a similar pedal feel as on a conventional braking system. On an actuation of the brake pedal 10, the signals from the sensor means 12,26,28 are evaluated within the electronic control unit (s) to determine the driver's braking demand. The electronic control unit (s) control (s) the valves 14a to 14d, valve 40 and the pump unit 16,18 for modulating the brake pressure in the wheel brakes 18a to 18d in dependence on the driver's braking demand. For closed loop control operations, the brake pressure in the wheel brakes 18a to 18d is sensed by the sensor means 24a to 24d in each case.

According to this embodiment of the invention, it is prescribed that the EHB system itself should respond to a non-critical fault in the EHB system by altering the pedal travel/applied braking force characteristic.

Fig. 3 shows a series of brake pressure (p) versus pedal travel (s) characteristic curves for different pedal behaviours. The thicker curve X represents the (normal) pedal characteristic when there is no fault condition in the system. Starting from the origin point of the axis system, the curve X increases progressively until reaching the maximum point SJP, T, where Sg is the maximum possible pedal travel and P, is the corresponding maximum brake pressure.

In accordance with the present embodiment, on a (non-critical) fault condition arising within the system, any one of a plurality of possible pedal behaviours can be generated by the electronic control unit (s) within the range of the rectangle defined by S, ;"and P, in accordance with control techniques, well known per se.

However, in all cases it should be guaranteed that the maximum brake pressure can be reached.

Four preferred embodiments of possible modified pedal behaviours are illustrated by the curves A to D in Fig. 3.

1. Curve A gives the driver the feeling of a so-called"long pedal". It runs continuously below the thick curve X and rises steeply in the end range of the pedal travel to meet the criteria of reaching the maximum point Smax/Pmax- According to this behaviour, the driver will notice a lower deceleration of the vehicle than usual, so he has to step on the brake pedal more. Also, he has to put a greater force on the brake pedal, for reaching the desired deceleration.

2. Curve B gives the driver the feeling of a so-called"short pedal". It runs continuously above the thick curve X and rises less steeply in the end range of the pedal travel to end in the maximum point S", a, / P", a, . According to this behaviour, the driver will notice a greater deceleration of the vehicle than usual, so he has to reduce the brake pedal actuation for achieving the desired deceleration.

3. Curve C also gives the driver the feeling of a"short pedal"but it has additionally a strong"jump-in"in the initial range of the pedal travel.

This will produce a pitching motion of the vehicle when actuating the brake pedal which is not comfortable for the driver and which causes him to go to a garage for checking the braking system.

4. Curve D gives the driver the feeling of a"very short pedal". It produces a very high deceleration of the vehicle and also shortens the pedal travel since the maximum point S,,./P,,. is shifted nearer to the brake pressure (p) axis.

The flexibility that any pedal behaviour can be generated within the range of the rectangle defined by S, l, a, and P, allows different fault conditions to be categorised with different pedal behaviours.

The above described embodiment is concerned only with fault conditions in the EHB system in which the EHB braking mode can be maintained. For example this could be a fault of one pressure sensor means 26 or 28, which are redundant. In fault conditions which occur for example on a breakdown of the electric power supply, the system is arranged to be switched into the already known so-called"push-through"mode by opening the valves 32a, 32b and closing valve 36 so that the pressure generated in the master cylinder 34 directly hydraulically acts on the wheel brakes 18a, 18b of one axle of the vehicle. In this event, the EHB system is unable to warn the driver of the fault. It is arranged instead that the steer-by-wire system causes the steering wheel to shake, independently on the road wheels, causing the driver to wish to slow the vehicle.

In other embodiments of the invention it can be arranged that the behaviour of more than one sub-control system is modified when a fault condition is detected. A first system may be modified for a period and then a second system is also modified. The first system may than revert to its normal behaviour or it may continue to behave in its modified mode. Alternatively, two or more systems may be modified together immediately on detection of the fault. The combination of systems and/or the sequence of their modification may be determined by the nature and/or severity of the fault to provide a weaker/stronger warning as appropriate and to air in diagnosis of the fault.

Fig. 4 shows an example of using normally undesirable pressure control on the brakes to give noise and vibration to warn of faults present. Graph A shows the normal pressure response to a demand. Graph B shows oscillations introduced on the apply part of the application. These will result in noise and vibration but will still allow good braking to occur.

Claims

1. A vehicle control system having a plurality of distinct function control systems, such as an electronically controlled braking system, a steer-by-wire system, an electronically controlled suspension system, an electronic engine management system and the like, wherein if a fault is detected in one such function control system, then that function control system and/or one or more other such function control systems is/are arranged to operate with a non-usual behaviour characteristic whereby to bring to the attention of a driver of the vehicle that a fault condition exists in at least one of the function control systems of the vehicle which needs remedial attention.

2. A vehicle control system as claimed in claim 1, wherein the behaviour of the function control system having the fault is modified.

3. A vehicle control system as claimed in claim 1 or 2, wherein the behaviour of a function control system not having the fault is modified.

4. A vehicle control system as claimed in any of the preceding claims, wherein the degree of the modification of behaviour varies over time.

5. A vehicle control system as claimed in claim 4, wherein the degree of the modification of behaviour increases over time.

6. A vehicle control system as claimed in claim 4, wherein the degree of the modification of behaviour varies randomly or pseudo-randomly over time.

7. A vehicle control system as claimed in any of the preceding claims wherein the behaviour is modified initially to a degree dependent upon the nature of the fault.

8. An electronically conrolled vehicle braking system of the type capable of operating in a brake-by-wire mode wherein hydraulic pressure is applied to braking devices at the vehicle wheels in proportion to the driver's braking demand as sensed electronically at a brake pedal, and in a push through mode wherein hydraulic pressure is applied to the braking devices at the vehicle wheels by way of a master cylinder coupled mechanically to the brake pedal, the electro-hydraulic braking system being operatively connecte to one or more other vehicle control system such that when a fault of a prescribed category is detected in the braking system, eithersaid braking system is itself arranged to adopt a modified operational characteristic behaviour, or at least one of said one or more other vehicle control systems is arranged to adopt a modified operational characteristic, the modifications of behaviour characteristic being of such a nature as to be likely to be notable by the driver.

9. A vehicle control system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

10. An electronically controlled vehicle braking system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.