Construction and Operation of Main Components Steering Column General
A motor, reduction mechanism, and torque sensor are mounted on the steering column.
Top View
Top View
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- Cross Section
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2) Motor
• A low inertia, low noise, and high power output motor is used.
• The motor consists of the rotor, stator, and motor shaft.
• The torque that is generated by the motor is transmitted via the joint to the worm gear. Then this torque is transmitted via the wheel gear to the column shaft.
• The rotation angle sensor consists of resolver sensor, which excels in reliability and durability. The rotation angle sensor detects the rotation angle of the motor and outputs it to the EPS ECU. As a result, it ensures efficient EPS control.
Worm Gear Motor Shaft
Rotor
Worm Gear Motor Shaft
Rotor
Rotation Angle Sensor
Column Shaft
Rotation Angle Sensor
Column Shaft
Wheel Gear 3) Reduction Mechanism
• This mechanism reduces the speed of the motor via the worm gear and the wheel gear, and transmits it to the column shaft.
• The wheel gear is made of a high strength, low friction, and low wear plastic material, to realize low noise and a lightweight construction.
• A worm gear supported by ball bearings is used. Also, a torsion spring is provided to ensure the optimal meshing of the gears at all times.
- Torsion Spring
Ball Bearing
Column Shaft
Wheel Gear
Ball Bearing
Wheel Gear
Column Shaft
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4) Torque Sensor
• The torque sensor detects the twist of the torsion bar, calculates the torque that is applied to the torsion bar by changing it into an electrical signal, and outputs this signal to the EPS ECU.
• Detection ring is mounted on the input shaft, and stub shaft is mounted on the output shaft. The input shaft and the output shaft are joined by the torsion bar. A detection coil is placed on the outside of the detection ring to complete an excitation circuit without making a contact.
• The detection coil consists of a dual circuit that outputs two signals, VT1 and VT2. The ECU controls the assist amount based on these two signals and at the same time detects a sensor malfunction.
- Detection Coil
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a. Straightline Driving
If the vehicle is driven straight and the driver does not turn the steering wheel, the specified voltage that is output at this time is determined by the EPS ECU to indicate the neutral position of the steering wheel. Therefore, it does not apply current to the motor.
b. When Steering
When a driver turns the steering wheel to the right or left, the twist that is created in the torsion bar creates a relative displacement between detection ring and the stub shaft.
This change is then converted into two electrical signals, VT1 and VT2, and sent to the EPS ECU. When the steering wheel is turned to the right, VT1 outputs a voltage that is higher than that of the neutral position.
Conversely, VT2 outputs a voltage that is lower than that of the neutral position. The direction of the turn is thus detected according to these outputs. Furthermore, the amount of steering assist is determined by the magnitude of the output value.
Voltage
Neutral Position during Straightline Driving
Neutral Position during Straightline Driving
- VT1
Left Turn
Assist Torque and Rotation Direction
Right Turn
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