With the mechanical connection removed in steer-by-wire, ensuring redundancy is vitally important to mitigate system failures. What is the strategy when a steer-by-wire system fails?
As the automotive industry moves towards electrification & autonomous driving, steering, braking, and suspension are three critical systems driving developments in vehicle dynamics, and the by-wire revolution is increasing vehicle functionality. Additionally, as chassis control technology becomes more mature, there is more focus on optimising cost efficiency, without compromising performance, functionality, and safety.
Redundancy is the main focus for steering technology developments, but there is still work to be done to define optimal redundancy levels that are sustainable in terms of cost and efficiency, whilst meeting necessary safety requirements.
The strategy when a steer-by-wire system fails depends on the specific design of the system. However, there are some general strategies that are common to most steer-by-wire systems:
- Redundancy: Most steer-by-wire systems use redundant angle sensors, actuators, and controllers to ensure that the system can continue to operate even if one component fails. For example, a steer-by-wire system might have two steering wheel angle sensors, two actuators, and two controllers. If one of these components fails, the other components can take over and the system can continue to operate. Redundancy is one of the most important strategies for ensuring the safety of a steer-by-wire system. For instance this is very important and mandatory in formula racing. By having redundant components, the system can continue to operate even if one component fails. This is essential for safety, as it prevents the driver from losing control of the vehicle. collaboration between OEMs and Piher has proven to increase robustness and reliability of sensors for SbW.
Simple redundancy and full redundancy are two different approaches to increasing the reliability of a system by duplicating critical components.
Simple redundancy (also known as N+1 redundancy) involves having one more backup component than the minimum number required for the system to function. For example, a server with two power supplies would have a simple redundancy of one, because it has three power supplies in total (two primary and one backup). If one power supply fails, the system can continue to operate on the other two power supplies.
Full redundancy (also known as 2N redundancy) involves having two copies of all critical components. For example, a server with two power supplies would have full redundancy, because it has two power supplies in total, and both power supplies are identical. If one power supply fails, the system can continue to operate on the other power supply without any interruption.
Simple redundancy is a less expensive way to increase the reliability of a system than full redundancy. However, simple redundancy provides less protection against component failures. If two or more critical components fail at the same time, the system will fail even if it has simple redundancy. Full redundancy provides more protection against component failures, but it is more expensive.
The best approach to redundancy for a particular system will depend on the criticality of the system, the budget available, and the risk tolerance of the organization. For example, a system that is critical to the safety of people or the environment would likely require full redundancy, even if it is more expensive. A system that is not as critical may be able to get by with simple redundancy, which is less expensive.
Here are the key differences between simple redundancy and full redundancy:
|Number of backup components
|One more than the minimum number required for the system to function
|Two copies of all critical components
|Protection against component failures
|Systems that are not critical or that have a budget constraint
|Systems that are critical or that have a high risk tolerance
- Fail-safe mode: Many steer-by-wire systems have a fail-safe mode that is activated if a failure is detected. In fail-safe mode, the system reverts to a mechanical steering system. This ensures that the driver can still steer the vehicle even if the electronic system fails. Fail-safe mode is another important safety feature for steer-by-wire systems. In fail-safe mode, the system reverts to a mechanical steering system. This ensures that the driver can still steer the vehicle even if the electronic system fails. Fail-safe mode is typically activated if a critical failure is detected, such as a failure of the steering wheel angle sensor or the actuator.
- Warning system: Steer-by-wire systems typically have a warning system that alerts the driver if a failure is detected. This warning system gives the driver time to take corrective action before the system fails completely.
The specific strategy that is used when a steer-by-wire system fails will depend on the specific design of the system. However, the strategies described above are common to most steer-by-wire systems. A warning system is also an important safety feature for steer-by-wire systems. The warning system alerts the driver if a failure is detected. This gives the driver time to take corrective action before the system fails completely. The warning system typically includes a visual warning light on the dashboard and an audible warning chime.
Piher offers innovative non-contact sensing solutions designed to reduce risk of failure on a wide variety of battery-powered construction equipment, including slewing and track drives on excavators, wheel and track motors on compact track loaders, skid steers, wheeled excavators and mobile elevating work platforms (MEWPs).