No Longer Science Fiction

Some original equipment manufacturers are re-engineering traditional vehicle hydraulic systems with intelligent electrical systems that reduce complexity and improve performance. Non-hydraulic or electro-hydraulic systems are inherently clean, quiet to operate, efficient and allow for more ergonomic design and less complex installation during the manufacturing process.

A natural consequence of the electrification of vehicles is the switch from standard hydraulic steering to all electric, or by-wire, steering systems. In many of these applications, tactile feedback devices (TFD) for by-wire steering systems are gaining acceptance with design engineers who are seeking solutions to today's trends: adopt vehicle designs based on electrical technology while maintaining the operator/machine interface that can mimic the feel of traditional hydraulics. In by-wire-steering systems, sensing of the steering command is required; however, many engineers are finding that safety and control are enhanced with controllable steering feedback.

These engineers view tactile steering feedback as a requirement in any by-wire implementation since it allows the operator a heightened sense of vehicle control and improves safety in operation. So, how does one get started in applying steer-by-wire systems to tomorrow's designs without starting from scratch? The key to success is identifying industry suppliers who are leaders in by-wire implementation and by applying lessons learned from other applications in order capitalize on the benefits of by-wire systems.

By-wire basics

Without the traditional mechanical steering link, developers of by-wire controls found early on that the loss of tactile feedback often results in a degradation of control via over or under steer, thus compromising safety and reducing productivity. To overcome this problem, a controllable and proportional force feedback device is connected to the operator steering control to produce useful tactile information, often mimicking the feel of the conventional system being replaced. The controller is programmed with a tactile feedback algorithm that modulates torque feedback to the operator as a function of steering wheel rotational position, velocity, acceleration, steered wheel position, vehicle speed, or other parameters — singly or in combination.

It is less expensive for an OEM to route wires than hydraulic hoses and from an ergonomic standpoint, reduced effort, variable rate/ratio steering can have the benefit of reducing whole arm and wrist fatigue that can occur from operating traditional multi-turn steering. By-wire steering is a great advantage in "man-up" vehicles where the operator is hoisted up to manually pick stock from high racks in the warehouse because it eliminates complex telescoping mechanical steering linkages.

Incorporating tactile feedback with steering sensing provides the option or possibility to communicate information to the driver regarding vehicle conditions. For example, tactile pulsing (high torque to low torque) while turning the wheel may indicate a vehicle fault or increased steering effort may indicate a vehicle obstruction. Vehicle warning systems, enstops (end of travel indication), and variable friction or variable steering effort (depending on machine mode of operation) provide more precise control by minimizing the possibility of oversteer/understeer and offer improved safety by providing more precise vehicle control. Furthermore, product standardization around common by-wire controls may decrease the cost associated with operator training and common vehicle interfaces can be adopted more easily.

Market need

According to Dr. Markus Plankensteiner, consortium coordinator for the TTA-Group (TTA is time-triggered architecture), the time is right for the development of reference architectures for on-road use. The TTA Group, a cross-industry consortium for dependable time-triggered systems, is working to develop such architectures for by-wire systems without mechanical backup for on-road use. The objective of the TTA-Group is to develop a global guideline to enhance reliability, interoperability and safety of steer-by-wire systems, which should lead to faster adoption and higher cost efficiency for suppliers and OEMs.