GB2400454A

GB2400454A - An ignition signal monitoring system for a vehicle.

Info

Publication number: GB2400454A
Application number: GB0308130A
Authority: GB
Inventors: Mark Ian Phillips; Mark Leighton Howell; Reza Shokoufandeh; Jonathan Charles Clarke
Original assignee: TRW Ltd
Current assignee: TRW Ltd
Priority date: 2003-04-09
Filing date: 2003-04-09
Publication date: 2004-10-13
Also published as: GB0308130D0

Abstract

An arrangement of electronic control units (ECU's) in a vehicle which are connected via a bus system for exchanging data there between. At least one of said ECU's receives the vehicle ignition signal directly and independently of the bus system. A check is conducted to whether the lack of the direct ignition signal at one such ECU is correctly indicative of the ignition being off. Derived from data available in the bus system is an additional signal representative of the ignition status. The ignition status signal is preferably derived from data such as engine RPM, wheel RPM. Preferably a CAN (central area network) bus system is used. The detection of the ignition signal is preferably required for safety, in order to initiate an emergency system shut down when a particular ignition signal detection has not occurred. This safety shut down may be required for an electrohydraulic brake (EHB) system, whereby mechanical breaking is allowed at lower decelerations.

Description

IMPROVEMENTS TO ROAD VEHICLE

BRAKING SYSTEMS.

The present invention relates to electronic control units (ECUs) which are connected via a bus system for exchanging data within the braking system of a road vehicle.

Electronic bus systems generally comprise a bus wire with at least two signal transmission wires, terminating resistors at either end of the transmission wires and a plurality of ECUs which are connected to the signal transmission wires between opposing terminating resistors of the bus wire and are adapted to transmit and receive electric signals via the transmission wires. Such a system can be commonly found in modern road vehicles, where the ECU of the braking system, the engine management system, the body control system etc all communicate via a bus system.

A drawback of a bus system is that it has no redundancy (i.e. even a small defect in the bus wire, e.g. a fracture, may result in the function of the entire system being jeopardised).

It is an object of the present invention to improve the monitoring of the ignition signal (SIGN) which is fed to an ECU, independent from the bus system, in order to obtain a higher reliability of the system.

In accordance with the present invention, there is provided an arrangement of electronic control units (ECUs) in a vehicle which are connected via a bus system for exchanging data therebetween, at least one of said ECUs receiving the vehicle ignition signal directly and independently of the bus system, wherein in order to check whether the lack of the direct ignition signal at one such ECU is correctly indicative of the ignition being off, there is derived from data available in the bus system an additional signal representative of the ignition status.

In some embodiments, said additional signal is derived from the ignition signal fed directly to another of said ECUs and passed to said one such ECU via the bus system.

In other embodiments, said additional signal is derived from data available on the bus system not corresponding directly to an ignition signal.

In one embodiment of the latter arrangement, for example, the additional signal is derived from a detection of information in the bus system indicative of the engine running.

A specific embodiment of the present invention will be hereinafter described by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic representation of the ignition signals received by the ECUs; and Figure 2 represents part of the ECU's control algorithm.

CAN is a standardised method of interconnecting ECUs to a system and was developed for the automotive industry. In a CAN system a number of ECUs exchange, in a digital manner, information via a bus wire consisting of a two-wire cable.

Normally each ECU has an independent power supply (URA1T) from that of the bus system. Furthermore, the ignition signal (SIGN) is fed to some ECUs independently of the bus system. Some systems must operate even when the ignition is OFF, which usually indicates that the vehicle is at standstill and the driver is entering, or intends to leave the vehicle, or has already left. For example the ECU of an electric parking brake (EPB) must be operational when the ignition is turned off to hold safely the vehicle at standstill and the ECU of a brake-by-wire system of the type such as an electrohydraulic brake (EHB) or an electromechanical brake (EMB) must be operational in wake-up and stand-by modes respectively, to be able to guarantee brake applications when the ignition is off. The ignition signal (SIGN) is required by some ECUs to maintain normal operation in the absence of the wake-up signal, or to allow different operating modes only when the ignition is turned on. Therefore, the ignition signal (SIGN) is of high relevance for the system safety, which is why it is monitored by the respective ECU.

In the case when the respective ECU does not receive an ignition signal (SIGN), it normally switches down to a failsafe mode and a visible and/or audible warning is given to the driver to indicate to him that the system performance is greatly restricted.

In the case of an electrohydraulic brake (EHB), the system may shut down to an emergency mode, which only allows manual braking at lower decelerations sufficient to fulfill legal regulations.

In the present example of the present system illustrated in Fig. 1, from data which is available already on the bus system, an additional signal (SIGN BUS) representing the ignition status can be derived. The additional signal (SIGN BUS) can be (1), the ignition signal directly fed to another ECU, which is provided on the bus system by that other ECU, or (ii) a plausibility signal derived from data anyhow available on the bus system (e.g. if data on the engine speed is available this can provide positive confirmation that the ignition must be on.) The advantage is that an ECU which directly receives a signal indicating that the ignition is off or detects a fault in the ignition signal (SIGN) can decide depending on the additional signal (SIGN BUS)' whether or not the ignition "really" is turned off, and therefore whether or not the ECU really does need to shut down into an emergency mode. Since then its normal operating mode can be maintained, the reliability of the system is essentially increased. If both signals indicate that the ignition is switched off, the vehicle can operate in a failsafe mode as in currently known systems. This decision making process is displayed in Figure2.

Claims

1. An arrangement of electronic control units (ECUs) in a vehicle which are connected via a bus system for exchanging data therebetwocn, at least one of said ECUs receiving the vehicle ignition signal directly and independently of the bus system, wherein in order to check whether the lack of the direct ignition signal at one such ECU is correctly indicative of the ignition being off, there is derived from data available in the bus system an additional signal representative of the ignition status.

2. An arrangement as claimed in claim 1, wherein said additional signal is derived from the ignition signal fed directly to another of said ECUs and passed to said one such ECU via the bus system.

3. An arrangement as claimed in claim 1, wherein said additional signal is derived from data available on the bus system.

4. An arrangement as claimed in claim 3, wherein said additional signal is derived from a detection of information in the bus system indicative of the engine running.

5. An arrangement of ECUs in a vehicle, substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.