Talk:Drive by wire

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I thought that "Drive by wire" was more than just throttle control. Isn't the purpose of the technology to "remove the mechanical linkages between the controls of a car and the devices that actually do the work"?

I think that the true drive-by-wire definition does involve exactly that, but that current implementations are far more limited in scope and thus obscure the real idea. I just posted this this on slashdot, but perhaps it has relevance here. --btrotter 05:25, 7 March 2007 (UTC)

[edit] Reliability

Airplanes have flown long time with fly-by-wire systems, and still comparable system for cars is considired unreliable? 193.167.107.251 (talk) 22:08, 26 November 2007 (UTC)

In general, yes. The airplanes have rigorous preflight checks and scheduled maintenance that would be not practical for a non-commercial road vehicle. The thought is any bugs or failures in the avionic computers will be detected, and programming and diagnosis is done in more of a "controlled environment" than thousands of semi-independent car dealers. A lot of work is being put in to this area though, and I would expect to see it in < 10 years. 128.147.28.1 (talk) 13:50, 22 March 2008 (UTC)

Systems designed to be safe are often less reliable than those that do not need to be safe. A fail-safe system will constantly perform self checks to ensure correct operation; these checks can pick up faults that would otherwise not have been noticed or the can be cause of failure themselves. As the system is fail safe it does not compromise safety but does lower reliability.

Safety critical systems that must maintain operation despite failures achieve this via redundancy. This redundancy makes the system 2 to 3 times as complex and therefore 2 to 3 times as likely to suffer a failure. The system is still safe as the redundant elements take over for the failed one, however the system will still need to be repaired and is therefore unreliable. The system has good availability, good safety but poor reliability and maintainability.

In cars throttle-by-wire makes sense as it reduced the number of actuators needed to implement features such as cruise control, traction control and hybrid operation. It reduced complexity and as a system it is inherently fail safe by using a spring to close the throttle on loss of power to the actuator. It is now very widely used and can provide additional features such as different throttle maps for different driving styles.

Brake-by-wire makes much less sense. Most additional functions desired can be achieved by modified stability control systems. Brake-by-wire systems must continue to function after a failure and are therefore not fail safe. The systems end up being much more complex for little additional benefit in conventional cars. Mercedes Benz used brake-by-wire in several models before abandoning it after significant reliability problems. It is possible that cars making use of regenerative braking will make brake-by-wire worthwhile.

Steer-by-wire offers very little benefit for a solution with a huge safety considerations that can only be tackled by adding massive cost and complexity to the steering system. Stated benefits include packaging and improved steering feel, however it is likely that both would be more difficult in a steer-by-wire system. SBW would need an actuator by the front axle, placing motors, sensors and electronics in the same area as the exhaust leaving the engine bay. The vehicles with the best steering feel have generally been those with the least technology applied, not the most. See any review of the non power steered Lotus Elise for details and contrast this with most reviews of cars with electric power steering.Maclauk (talk) 21:05, 28 May 2008 (UTC)