Steer-by-wire

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Among steer-by-wire , a system in which one understands vehicle technology , in which a steering command from a sensor (in particular the steering wheel ) only electrically to a control unit electromechanical actuator is, executes the steering command forwarded. In such a system there is no mechanical connection between the steering wheel and the steered wheels.

In aviation , the analog fly-by-wire with its high redundancy of the steering system has long been a reality; Steer-by-wire has been approved for passenger cars for some series vehicles, the main area of ​​application here is driving with disabilities. In contrast, such systems are quite widespread in special vehicles and as auxiliary steering systems (trailing steering axles).

advantages

  • Mechanical components are replaced by electrical components. This results in advantages in terms of installation space, assembly, the right-hand and left-hand drive variants and in terms of crash behavior.
  • The steering angle can be adapted to the driving dynamics. The function of the ESP can be extended to include a steering angle.
  • As with superimposed steering , it is possible to suppress certain disturbances, e.g. B. Ripple suppression, elimination of the yaw angle weakening with ABS, damping of crosswind offset.
  • The feedback forces to the vehicle driver can be set optionally.
  • Compared to conventional power steering , the auxiliary energy consumption can be reduced.
  • Variation of the steering behavior depending on the driving situation, e.g. B. understeering, oversteering or neutral.

Security aspects

If the system fails, it depends on the structure of the system whether the vehicle can still be steered. If the steering assistance is replaced by a servomotor in a classic system and the wheel angles are controlled via a steering trapezoid, the steering ability is not guaranteed in the event of failure.

Newer concepts therefore prefer individual servomotors for each wheel. In the event of a fault, only one motor is likely to fail, and the wheel can then be put into a straight-ahead position (fail-safe) in terms of design. The vehicle can then be steered by the second wheel, whereby ESP and the engine control can also generate steering torques to support the driver by distributing the braking and drive torques.

The current development in motor vehicle construction tends to forward all driver commands only electrically. Systems such as brake-by-wire , shift-by-wire and steer-by-wire are currently the subject of extensive research. Approval for steer-by-wire can only be expected in Germany and other countries when the manufacturers have proven that it is at least as fail-safe as conventional steering. Fulfilling this requirement in an economical production is the challenge in the development and the main reason why Steer-by-wire has only reached mass production readiness in individual cases.

Use in special vehicle construction

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Steer-by-wire has been known in special vehicle construction for around 40 years. The first systems were developed for heavy-duty vehicles in the 1970s. A so-called steering force simulator is used as the electronic steering wheel, which on the one hand detects the steering angle of the steering wheel and on the other hand simulates a variable steering force and a mechanical end stop by means of an integrated electrically operated brake. The steering movement is generated electronically and hydraulically via proportional valves, which are controlled by an electronic control unit. The steering angles of the wheels are read back via actual value transmitters, creating a closed control loop. Today, steer-by-wire steering systems are standard in all applications in which either several axles have to be steered with respect to one another in a certain geometry or the required steering forces for conventional steering with external power are too high. Another advantage of steer-by-wire technology is the ability to integrate lane guidance or navigation systems. Steer-by-wire systems are widely used in heavy-duty vehicles, aircraft tugs , straddle carriers , reach stackers and order picking forklifts .

Trailing steering axle

A special form of steer-by-wire is the so-called auxiliary steering system (ASE = auxiliary steering equipment). Here, the rear axle of a commercial vehicle is adjusted according to the steering angle specified by the main steering system (front axle). The direction of travel of the vehicle is conventionally specified via an externally assisted, mechanically driven steering system; rear axles are tracked in the sense of a mechanically decoupled, electronically controlled system. The steering angle of the front axle is recorded by a sensor. From the steering angle, the axle geometry and the vehicle speed, an electronic control unit generates a setpoint according to which the rear axle is usually steered via an electronic-hydraulic control circuit. Typical applications are three-axle buses, distribution trucks or mobile cranes. The steering of the rear axles, often trailing or leading axles , reduces tire wear and improves the maneuverability of the vehicle. The first auxiliary steering systems were presented by Mobil-Elektronik GmbH in the early 1980s .

Individual evidence

  1. ↑ Nissan brings steer-by-wire into series production. Article on heise.de from October 17, 2012

literature

See also