Sensor-Actuator Based Smart Yoke for a Rack and Pinion Steering System

The controlling behaviour of a vehicle is influenced by the performance of its steering system. The steering system consists of steering wheel, steering column, rack and pinion, steering gearbox, and a linkage system. The vehicle is controlled by the behaviour of the steering gear with the spring loaded rack and pinion. This spring loading arrangement consists of yoke nut, spring, and plunger. The plunger is always in contact with the rack, by the spring and yoke nut. The spring loading arrangement helps to eliminate the backlash between the rack and pinion, but increases the preload on the gear. This increases the torque required to rotate the steering wheel by the driver. In order to reduce this torque requirement, the spring loading can be reduced which in turn will increase the noise when the vehicle running on a bumpy road, and also may turn undesirably due to road disturbances. Hence, contradictory requirements to be fulfilled in the steering gear. This is done by providing an allowable preload on the spring. In practice, however, it will be desirable that the steering system is stiff while going on a straight road, and less stiff while turning at low speeds. This is accomplished by a Sensor-Actuator Based Smart Yoke for the rack and pinion steering system. In this arrangement, the sensor will sense the rack position. This sensor used here is a linear variable differential transformer (LVDT). The sensor signal is captured by LabView software, and according to the sensor data, the software calculates a signal for the DC servo motor, that rotates the plunger causing the change in spring loading. The LabView signal is calculated based on an empirical formula obtained from a real torque data required in the rack and pinion steering system.