Steer-by-Wire Systems with Integrated Torque Feedback Improve Steering Performance and Reduce Cost
- Wednesday, 01 June 2011
Electronic steering also provides far more opportunity in configuring the steering functionality of the vehicle. Design engineers themselves can easily change the steering ratio with a software command, and can even design the vehicle so that the steering ratio can be changed in the field or programmed to change on the fly, depending on vehicle operating conditions. For example, an electronic steering system could be configured to have a high steering ratio at low speeds and a lower ratio at high speeds to help avoid sudden turns at high speed, or configured to allow for rapid maneuvering at low speed. Electronic steering can be programmed to indicate that the vehicle is nearing the end of the steering range by increasing torque resistance. Electronic steering also opens up the door to other more advanced options such as using torque resistance to prevent the operator from steering towards detected obstacles.
Unique Torque Feedback
A critical consideration in moving to electronic steering is that operators are used to the tactile response, or “feel,” provided by both direct mechanical and hydraulic steering systems. The earliest generations of electronic steer-by-wire systems did not provide this feedback and they did not achieve acceptance by vehicle users. Today, torque feedback devices are available that provide several significant advantages. The new approach works much like a brake by using a magnetic actuation system to apply force to a friction disc that impinges upon a rotor. The friction disc utilizes an innovative material whose static-to-dynamic-friction performance is not subject to the slipstick effect that in a conventional brake generates a higher level of friction when the shaft is stationary.
The new material also provides a proportional torque force over a wide range of applied forces. The air gap between the friction material and the rotor remains constant regardless of wear to the friction material. Unlike other materials used in torque feedback devices, the new friction material is insensitive to temperature so it provides consistent performance over a wide range of operating conditions without the need for a temperature compensation system. The new material generates a consistent frictional force over its life and does not generate any frictional force when current is turned off. This torque feedback device also provides faster response to very small changes in current.
Integrated Systems Reduce Development Costs
Nearly every industrial utility and personal mobility vehicle manufacturer has either introduced steer-by-wire or has an initiative underway to introduce it in the near future. Many of these companies are designing and sourcing their own systems. This can be a challenging task because of the need to specify a sensor, building or buying a system to provide torque feedback, providing a drive motor, and integrating these components with each other and with the vehicle.
Utilizing a complete electronic steer-by-wire system can substantially reduce product development and sourcing costs while providing an advanced design that has been proven in the field. Such electronic steer-by-wire systems include redundant shaft position sensors, torque feedback device with friction assembly and electromagnetic actuator, drive motor, and protective housing. The original equipment manufacturer simply needs to connect the drive motor to their gearbox, bolt the steering wheel to the housing, and program the device to provide the desired functionality.
The architecture of these complete systems offers a wide range of mechanical interfaces, voltages, torques, drive horsepower, etc. as standard, so they can be adapted easily to most any application. Such integrated electronic steering systems are, in most cases, less expensive than hydraulic systems and internally developed electronic steering systems.
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