12-70000-00
1. SYSTEM DESCRIPTION
The power steering has been designed to make the wheel move more easily than in a manual steering
system. The hydraulic power assists the process utilizing hydraulic fluid. The fluid increases pressure in
the power steering pump and aids the movement of the steering mechanism.
The power steering system consists of pump, oil reservoir, rack and gear box.
The power steering pump is a vane type and delivers hydraulic pressure to operate the power steering
system.
The pressure relief valve in the pump controls the discharging pressure.
The rotary valve in the rack and the pinion gear directs the oil from the power steering pump to one side
of the rack piston. The integrated rack piston converts the hydraulic pressure to linear movement. The
operating force of the rack moves the wheels through the tie rod, the tie rod end and the steering knuckle.
Even though the hydraulic pressure cannot be generated, a driver can steer the vehicle without power
assist but it needs very high steering force.
In this case, the operating force of the steering wheel is conveyed to the pinion, and the movement of the
pinion moves the rack through the pinion gear combined to the rack gear.
12-8
Installation of steering
gear box and pipeInstallation of pipe
Installation of reservoir and hoseInstallation of power steering pump
and pipe
2. SYSTEM LAYOUT
The steering pump is driven by the engine power through a belt. This pump circulates the power steering
oil from the reservoir -> steering pump -> oil supply pipe -> steering gear box -> oil return pipe ->
reservoir to perform steering operations.
Return pipe
Supply pipe
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) ▶
