Law drives electronic brakes
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Almost every brake manufacturer is investigating electronic controls for braking systems. But the future of electronic braking systems (EBS) will depend on legislation and acceptance by truck operators, according to speakers at the Institution of Mechanical Engineers seminar on braking.
by Toby Clark • The IMechE event brought together most of Europe's brake manufacturers, and several of the truck builders that are introducing or investigating EBS. Every speaker was enthusiastic about electronic braking: Geoff Harvey of the Department of Transport—part of the team responsible for framing European braking legislation— said: "I am almost certain that F.:13,S will become mandatory".
Are operators willing to be convinced? Keith Moore of Iveco Ford approached this question with a survey, asking 60 truck drivers whether they wanted improved braking systems. Naturally, all said they did, particularly wanting control improvements such as consistent brake-pedal feel independent of load, and integrated exhaust/retarder/service brake operation. But operators are just as likely to have reservations about compatibility with existing systems, and the reliability of electronics. Chris Wiehen of Wabco (whose EBS system is fitted to the Mercedes Actros) put it bluntly: "EBS has to be reliable—if it fails at all in the first year it will have an image problem".
Pros and cons
EBS will only become popular with end-users by providing lower running costs: most delegates pointed out that brake lining life could be extended dramatically using techniques to even out wear across axles.
Many speakers pointed out that EBS would speed up response times and shorten stopping distances by around 10%. Other potential safety improvements include improved ABS operation, consistent operation whether brakes are hot or cold and better compatibility between tractor and trailer brakes.
EBS has advantages for manufacturers too: production varia
tions can be minimised, and modular design means that systems can be devised for many different types of vehicles, often with only some software changes. Standards already exist to combine different man ufacturers' systems the digital CAN bus is used for data transfer, while ISO 11992 governs the connection between tractor and trailer. However, Wabco's Dr Wiehen pointed out that "targets of simplification and cost reduction compared with conventional systems have yet to be met".
The legal framework for electronic braking is still uncertain: all EBS manufacturers at present are producing "hybrid" systems with pneumatically controlled backup should the electronics fail, as this is effectively required by law, But Geoff Harvey of the DOT said that this requirement would not necessarily be retained—the aim was to enforce minimum performance levels rather than introducing a design restriction. Existing rules do not define E13S, so the first stage is to rewrite them to distinguish clearly between electronic and pneumatic systems and between control and energy transmission.
Trials
Different manufacturers are taking different approaches to EBS: some are convinced that coupling force control systems (at: or CFCS) are desirable. These sense the horizontal and vertical forces in the trailer kingpin to control the balance of tractor and trailer braking. Others such as MAN claim CFC is too expensive, and are backing "smart" systems to calculate, rather than measure, trailer load.
Lucas is looking at different EBS set-ups in a long-term trial of three Volvo FLIO tractive units in operation with Swift Transport. Even a relatively simple system, using conven. tional trailers without CFC, gives useful improvements: the relationship between coupling head pressure and deceleration is much more consistent than usual, though CFC makes it even better. Lucas has also measured the brake boost required for a variety of rented trailers: most are acceptable, but an alarming number need up to 20% boost, while on the other hand several have been "highly over-braked". CFC can warn the driver if this is the case.
Another useful finding was that more than half of all brake applications are extremely gentle (less than 5% retardation) while less than one in 100 applications has to be over 20%. EBS can be set up to provide evenly-distributed braking (and minimal brake wear), only switching to maximum retardation (with braking biased to the front) when the pedal is applied hard.
Future developments
But EBS systems can be far more sophisticated: they may incorporate traction control, or even Vehicle Dynamic Control (VDC), which involves braking each wheel individually to improve stability. Other suggestions range from improving hill starts—Iveco's survey indicated that 80% of drivers would like a "hill-holder" system—to Autonomous Intelligent Cruise Control. AICC would keep a safe distance between trucks automatically: the European Chauffeur programme (involv ing most of the producers of EE3S) aims to demonstrate such a convoy on the Brenner autoroute by the end of 1998.
There was even talk at the seminar of fully electric braking systems, doing away with pneumatics altogether—but unlike EBS, these are a long way off.
C Seminar papers from the event (ISBN 1 86058 036 X) are available from the IMechE on 01284 763277.