Control steering-angle sensors

The vision of braking and steering by wire will demand new, extremely reliable sensors. Even in early implementations of steer-by-wire systems, in which manual control can override any system failure, more than one sensor is normally used for the sake of redundancy. Many of the sensor principles required are already established in the market, including steering-angle sensors (e.g., for vehicle dynamics control) and pedal-position sensors. Mechanical action or feedback control, however, will drive the emergence of torque and force sensors. 

The MR fluid-based suspension systems implemented on these various vehicles enable simultaneous ride comfort control and body motion control. As indicated in Fig. 6.85, the control system architecture for these systems processes inputs from relative position sensors at each wheel. In addition, inputs from a lateral accelerometer, yaw rate sensor, steering angle sensor and speed sensor all feed by way of a CAN BUS into the controller. The control algorithms are quite complex and seek to simultaneously optimize a wide range of performance features including overall handling, overall ride comfort, body control, road noise, head toss and a subjective safe feeling. 

One high-volume application is the wheel speed detection for anti-lock braking (ABS) systems. Wheel speed information is also needed in modern vehicle dynamics control (VDC) and navigation systems. Both require, in addition to the wheel speed, the steering angle as an input value, which is also often provided by magnetic sensors. A classic field of application is the power train, in which magnetic sensors deliver information about the cam and crank shaft positions as well as the transmission speed. 

SAS will be needed in future applications such as EPS, AFS, and SbW. These systems need a torque sensor to measure the steering torque applied by the driver in order to control an assisting torque. Hence a combination of SAS and torque sensor seems to be obvious. Products combining angle and torque measurement have been proposed (e.g., an opto-electronic angle and torque sensor for integration in EPS and EHPS systems [29]). 

A directional SHM transducer that does not require either phase-array delays or connection switching to achieve steering is described in Xu et al. [63]. This directional sensor achieves tuning into preferential direction at certain discrete frequencies, which are the solution of a firequency-wavenumber equation. The transducer consists of a skew array of piezo-wafer active sensors placed at pitch values d, d.2 and angles a, 5 about the 1 and 2 axes, respectively (Figure 16.29(a)). The transducer achieves directivity at certain fi equencies Figure 16.29(b) illustrates the directionality measured with SLDV on an isotropic aluminum 45° at 105 kHz, 120° at 150 kHz, — 17° at 200 kHz, 88° at 280 kHz. Thus, the transducer directionality is controlled by the excitation firequency in discrete steps. 

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