Talk:Drive by wire

From Wikipedia, the free encyclopedia
Jump to: navigation, search

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"?

Reliability[edit]

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)

Toyota Prius[edit]

I have removed this section because the prius is not the current state-of-the-art in drive-by-wire. It has an entirely standard throttle and transmission control system. The braking system is a standard hydraulic system with additional regenerative braking so this is not considered as brake-by-wire.Eeyrsja —Preceding unsigned comment added by 94.192.58.182 (talk) 12:52, 14 January 2009 (UTC)

Sounds good. But don't forget some Priuses have computer controlled electric steering along with the traditional system. Although not strictly steer-by-wire for this reason, it's still very unusual to have electronic steering control at all so must surely be interesting to people looking up drive-by-wire. Kallog (talk) 01:39, 17 January 2009 (UTC)

Not at all. It is very common to have electrically powered steering with a large number of suppliers of this type of system. The Mazda 2, Ford Fiesta, Nissan Micra, Nissan Cube, Renault Clio, Renault Megane, Renault Modus and Fiat Bravo all use the same core electronically controlled EPS system.--Maclauk (talk) 13:54, 1 July 2009 (UTC)

The Toyota Prius is actually very by-wire. The throttle system uses an Electronic Throttle Control System just like most Toyotas and the Prius e-CVT transmission has to be controlled by-wire because it doesn't have any mechanical control mechanism. Starting with the 2004 model Toyota adopted an "Electronic Controlled Braking" system which is an electro-hydraulic brake-by-wire system with an integrated mechanical back-up (bypass valve) if power fails. When the power is on there is no direct connection between the pedal and the friction brakes. This brake system is similar to the ones Mercedes dropped.Prius Technical Overview --Warpshock (talk) 23:07, 27 January 2010 (UTC)

Throttle Lag[edit]

The Disadvantages section says there's an inherent delay that causes poorer response. Any source for this? A look on Google seems to say there are artificial delays to improve fuel economy and reduce shock loads on the drive train, but nothing about an 'inherent' delay. You can buy after-market kits to speed it up, which shows ETC isn't the problem.

This other article implies ETC actually improves response with multiple throttles closer to the engine. Kallog (talk) 11:10, 30 September 2009 (UTC)