-A pinion-assistant type EPS system is employed. -The EPS system is sensing vehicle speed. -The EPS system is controlled at all vehicle speed range. -By employing the pinion-assistant type, EPS motor is unified with steering gear box. -EPS control module is separated from the steering column assembly.
The steering gearbox was newly developed. It has superior mounting rigidity that helps to realize a positive steering feel. Plus, the power-assistance unit is located outside the cabin so the cabin is relatively quiet.
This table shows the function of each components. There is nothing different from the existing models.
Steering gear case consists of input shaft, output shaft, torsion bar, torque sensor, worm gear & wheel and EPS motor. The steering gear case is supported by front suspension frame.
The torque sensor is a non-contact variable inductance type. When the steering wheel is turned, the torsion bar between input shaft and output shaft is twisted. This torsion creates an axial movement of the core (3). In right turning, the core goes up and the inductance of coil 1 (1) varies. In left turning, the core goes down and the inductance of coil 2 (2) varies. This variance of inductance is detected by the amplifier (4) of the torque sensor. The torque sensor outputs the voltage signals to EPS control module. The amplifier (4) consists of double circuits, one of which is main (5) and the other is sub (6). EPS control module calculates the steering torque and direction by using these two signals. The EPS control module calculates an average value of the voltages obtained by main and sub signals. The average value is used as steering torque. The steering direction is detected by comparing the average value with 2.5 volts.
If some malfunction* occurs in EPS system, EPS system works as a manual steering, i.e. without power assistance. Also when the engine is at stop, the system works as a manual steering. [Manual Stopper Operation] When the steering wheel is turned, the torsion bar is twisted. As the power supply to the EPS motor is cut off, there is no power assistance. If the steering wheel is further turned, the driver ’ s force is directly transmitted to the output shaft (pinion shaft) via manual stopper part. Note*: In case of VSS malfunction, EPS provides a minimum power assistance.
EPS motor is equipped with a torque limiter. If an excessive torque input (impact torque) occurs at a tire, the torque limiter absorbs the impact to protect the EPS motor and gear. [Torque limiter operation] 1.An excessive torque (impact torque : 5a) is transmitted from a tire to worm gear (3). 2.The impact torque (5a) is transmitted to the boss (4e) which is spline-fitted to the worm gear (3). 3.If the impact torque(5a) exceeds the specified value (5b), a slip occurs between the boss (4e) and the friction plate (4d) which is fixed to the motor (1). The yellow zone in the graph shows the slip zone.
The terminal E52-17 sends power steering signal to ECM when the steering wheel is turned.
EPS control module determines the basic assistant force by steering assistance control. EPS control module corrects the basic assistance force by adding inertia compensation, handle return and steering attenuation controls to improve the feeling of steering. According to the results of these controls and maximum current regulation, the EPS control module calculates the target current. Then the EPS control compares the target current and the measured value to adjust the current.
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