Steer-by-Wire Systems with Integrated Torque Feedback Improve Steering Performance and Reduce Cost
- Wednesday, 01 June 2011
Hydraulic steering systems have long dominated the industrial utility vehicle market because of their familiarity both to vehicle designers and operators. More recently, a trend has been seen towards the use of electronic steer-by-wire systems that provide greater design flexibility by enabling software to customize the connection between the steering wheel and steering mechanism. Several suppliers offer integrated steer-by-wire systems targeting the industrial utility vehicle market. A key differentiating factor is the method used to provide torque feedback to give the operator a heightened sense of vehicle control. The latest generation of integrated steer-by-wire systems consumes less power, is less expensive, and offers the ability to be programmed to provide a wide range of value-added features.
Moving Away from Hydraulic Steering
Hydraulic steering technology has been used in industrial utility vehicles for decades. Engineers are familiar with its ruggedness in unfriendly environments and its power density, which enhances performance in the most difficult applications. But recent trends in the industry position hydraulic steering as less advantageous for many industrial utility vehicles. Hydraulic steering systems require a motor, pump, valves, hoses, and fittings. Utility vehicles that utilize hydraulic drives for other functions may or may not have a hydraulic pump with enough capacity to accommodate the steering system.
There has been a general trend away from hydraulics in other applications as well. Many manufacturers are looking to cut back or eliminate the use of hydraulics, so it is becoming much harder to find spare capacity on a hydraulic pump for the steering system. If spare capacity is not available, then it becomes necessary to add a hydraulic system dedicated to steering, which substantially raises the cost of this approach. Electronic steer-by-wire systems, on the other hand, are completely self-contained and do not require external pumps or hoses. This means that they are usually considerably less expensive than hydraulic steering when the costs of the pump, valve, hoses, and fittings are taken into account.
Another reason for considering a move away from hydraulic steering is the desire to improve battery life of electric-powered vehicles and reduce energy consumption of fossil-fuel-powered vehicles. Hydraulic vehicles tend to consume relatively high amounts of power because the hydraulic system continually consumes supply power whether or not the steering system is being operated. Electronic steering also consumes considerably less power because power is drawn only when operating the steering systems.
Advantages of Electronic Steer-by-Wire Systems
Another reason for the trend away from hydraulic steering is substantial performance improvements that have been made in electric motors. The power density of electric motors has substantially increased because of advances in magnetic materials, lead/ball screw efficiency, construction, manufacturing techniques, and electronics. Today’s electric motors can deliver substantially more power while maintaining high levels of efficiency. Steer-by-wire systems have also benefitted by the improved reliability of all electronic and electrical products. Electronic steering systems provide nearly maintenance-free operation and are much less prone to fail due to lack of maintenance.
Electronic steering also offers substantially greater design flexibility than hydraulic or direct-drive systems. There is much greater flexibility in locating the steering wheel because it no longer has to connect directly to a mechanical drive shaft or a hydraulic valve, which in turn needs to be connected by hoses to the steering motor. Electronic steering eliminates the need for costly telescopic mechanical linkage or long hydraulic hoses in man-up vehicles where the operator is hoisted up to pick stock from high warehouse racks.