Drive-By-Wire: Mechanism, Protocol and Performance

By Vandana R Mesta, B.E.(E&C), AIT, Chikmagalur

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It has a data rate up to 10 Mbps (redundant single channel mode). The flexible, expandable FlexRay network consists of up to 64 nodes connected point-to-point or over a classical bus structure. For physical transmission medium both optical fibres and copper lines are suitable. FlexRay (like CAN) is a receiver selective bus system, that uses cyclic TDMA (Time Division Multiple Access) method for data transmission control. FlexRay frame structure is as shown below.

FlexRay allows both synchronous (real-time) and asynchronous data transfer to meet the demand for various systems in vehicles. It also allows synchronous transmission, for non-time critical data via freely configurable, static and dynamic time segments. Its error tolerance is achieved by channel redundancy checksum that detects and handles logical errors.

Advantages of by-wire systems

Drive-by-wire will be a new experience for drivers: some might get excited and others might get scared at first. Now the question is why go for by wire systems?

Improved performance, efficiency, reduced emission and fuel economy:

Because of full communication loop the vehicle can respond faster and more efficiently to changes in the operating conditions.

Saves weight and raw materials:

By-wire components can become much smaller compared to mechanical components; by-wire steering and braking systems are more significant.

Packaging advantages:

Designers can enjoy a great level of freedom (it won’t be necessary to locate the brake booster or steering column in their usual places).

Consistent, reliable operation over the life of the car:

fewer moving parts and better isolation from vibration and the elements. In case of failure like wear, break or snagging of the throttle cable, intelligent operation will keep the throttle from ever ‘sticking’ open, and if the throttle system fails it is linked to the vehicles diagnostic system.

Makes active safety measures possible:

faster, more accurate interfacing with stability control systems and ‘smart’ cruise control. Also, there is space for future active safety measures like collision avoidance systems and park assist gadgets.

Integrates vehicle systems:

This feature is unique for by wire systems. For instance, a vehicle’s airbag system could consider the throttle position at the time of impact or release the throttle in an impact. An automatic suspension system could stiffen in response to a punch of the gas or the steering system could take throttle position into account when deciding how much boost to give.

Although we can enjoy these benefits we can’t neglect the following drawbacks:

  • They are costly
  • They have to be standardized
  • Only factory trained mechanics can understand how to fix/replace these components
  • Use of overtaxed, standardized 42V systems
  • Vehicular communication security problems

Future of drive-by-wire systems

Suitable measures must be taken to overcome the drawbacks. Since future automotive systems and business models particularly depend on comprehensive and efficient measures that provide vehicular communication security, adequate technical, organizational and financial expenditures must be arranged today.

Here are a few milestones in this area. The first production vehicle to implement this was the Infiniti Q50. Its implementation in road vehicles is limited by concerns over reliability although it has been demonstrated in several concept vehicles such as ThyssenKrupp Presta Steering’s Mercedes-Benz Unimog, General Motors’ Hy-wire and Sequel, Saabs Prometheus and the Mazda Ryuga. The Swedish startup Uniti will release the Uniti all-electric car in 2019 with an in-house designed steer-by-wire system which will be entirely replacing the steering wheel. The concept was showcased in VR at the 2016 CeBit edition.


 

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