Steering: Description and Operation

POWER STEERING: POWER STEERING SYSTEM: SYSTEM DIAGRAM

SYSTEM DIAGRAM





Communication table





*1: w/o Multi-information Display
*2: w/ Multi-information Display

POWER STEERING: POWER STEERING SYSTEM: SYSTEM DESCRIPTION

SYSTEM DESCRIPTION

1. GENERAL
(a) The power steering system uses a power steering motor, a power steering torque sensor and a reduction mechanism that are built into the steering column assembly to generate assist torque in order to assist the driver's steering effort.
(1) This system activates the power steering motor only when the driver turns the steering wheel. As a result, no energy is consumed when the vehicle is going straight, enhancing fuel economy.
2. FUNCTION OF MAIN COMPONENTS
(a) The power steering system components function has the following:





*: w/ Multi-information display
(b) Steering Column Assembly




(1) The steering column assembly includes a power steering torque sensor, power steering motor, and reduction mechanism.
(c) Power Steering Torque Sensor




(1) Power steering torque sensor consists of the sensor sleeve, stub shaft and detection coil. This sensor outputs 2 types of signals to the power steering ECU.

- The sensor sleeve is mounted on the input shaft, and the stub shaft is mounted on the output shaft. The input shaft and the output shaft are joined by the torsion bar.
- The detection coil assembly is placed on the outside of the sensor sleeve to complete an excitation circuit without making a contact.
(2) Steering Torque and Steering Direction Detection





- When the steering wheel is not turned:
When the driver does not turn the steering wheel, the power steering torque sensor outputs a specified voltage (2.5 V) to the power steering ECU. As long as the specified voltage is output, the power steering ECU determines that the steering wheel is in the neutral position.

- When the steering wheel is turned:
When the driver turns the steering wheel to the right or left, twist that is created in the torsion bar creates a relative displacement between the sensor sleeve and the stub shaft. At this time, the voltage output from the torque sensor to the power steering ECU changes. Based on the changes, the power steering ECU determines the steering torque and steering direction input by the driver.

(d) Power Steering Motor




(1) A low inertia, low noise, and high power output power steering motor is used.
(2) The motor consists of the rotor, stator, motor shaft and rotation angle sensor.
(3) 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.
(4) The rotation angle sensor consists of the resolver sensor, which excels in reliability and durability. The rotation angle sensor detects the rotation angle of the motor and outputs it to the power steering ECU. As a result, it ensures efficient EPS control.
(e) Reduction Mechanism




(1) This mechanism reduces the speed of the power steering 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.





(f) Multi-information Display
(1) The multi-information display shows a warning message to inform the driver that there is a malfunction in the power steering system.

3. SYSTEM CONTROL
(a) General
(1) The power steering system has the following controls:










(b) Basic Control
(1) The power steering ECU receives the vehicle speed signal and signals from various sensors. Based on these signals, the power steering ECU judges the current vehicle condition, and determines the assist current to be applied to the power steering motor.

- The diagram below describes the relationship between the steering torque and the assist power current.

(c) Diagnosis
(1) If the power steering ECU detects a malfunction in the power steering system, the power steering ECU lights up the P/S warning light in order to alert the driver. At the same time, DTCs (Diagnostic Trouble Codes) are stored in memory.

- These DTCs can be read by connecting Techstream to the DLC3 Reading and Clearing Diagnostic Trouble Codes.

(d) Fail-safe
(1) Fail-safe operation modes are as follows: