13-6
Hydraulic power steering Electric power steering
1. OVERVIEW
The electric power steering, EPS, does not have any belt-driven steering pump constantly running, so it
is lightweight and the motor consumes energy only when the steering wheel is turned by the driver, and
this leads to improvement in fuel efficiency. Also, the elimination of a belt-driven pump and its
accessories greatly simplifies manufacturing and maintenance. While offering these benefits, as it does
not contain any steering oil, the environment is not polluted both when the steering system is produced
and discarded.
In other words, the electric power steering (EPS) system uses the electric motor to assist the steering
force. It functions independently regardless of whether the engine is running or not, unlike the existing
hydraulic power steering.
The EPS system generates an assist steering force variably depending on the driving conditions by
controlling the motor's operation, based on the input signals from the sensors such as torque sensor and
angle sensor. In turn, the EPS receives the torque signal by the driver's movements of the steering
wheel, as well as the vehicle speed, and uses the motor to determine the assist torque. The EPS
controls the motor for this. Another features of EPS are fail-safe function, diagnosis function,
communication function between units and interface function for external diagnostic device.
The EPS system components such as the torque sensor, steering angle sensor, fail-safe relay, etc. are
located in the steering column and EPS unit assembly.
Advantages: ▶
Assurance of improved steering
Provides optimal steering force according to the
vehicle speed
Enhanced steering stability while driving at high
speed (1)
-
-Reduced fuel consumption
Consumes energy only when steering wheel
is turned (improved by 3 to 5%)
Energy saving (reduced by 85% compared
with hydraulic power steering)
Reduced number of parts: Elimination of
steering pump, hydraulic hose, pump pulley,
oil reservoir, belt, bracket, etc. (2)
-
-
-
Comparison between hydraulic power steering and electric power steering (EPS) ▶
02-158810-00
Collision signal interface ▶
The open collector driver raises or lowers the voltage of the pin no. 58 by switching on and off the drive
transistor. The vehicle module can be operated normally only by the logic of open collector interface
and can be maintained in a pull-up state. The followings are the specifications of the electrical interface.
The load resistance of the SDM is 590 ohms or higher. It may not be possible to operate the collision
occurrence circuit normally if the resistance value is not as specified.
Pin No. Minimum Average Maximum Remark
Driving current (current value
when the transistor is turned
on) 12.31 mA 19.6 mA 30 mA Depending on the
battery voltage
Leakage current (current value
when the transistor is turned
off) 147.6 μA 376 μA No crash signal
Load resistance 590 ohms Above than this value
