Power Steering System (Power Steering System)

A power steering system adds a power-assist mechanism onto a conventional mechanical steering setup. Its primary purpose is to reduce driver steering effort while dynamically varying the level of steering assistance according to vehicle speed, delivering effortless manoeuvring at low speeds and reassuring stability at high speeds.

System Classification

Currently, there are three primary types of power steering systems available in the market:

Hydraulic Power Steering (HPS - Hydraulic Power Steering):

Working Principle: The engine drives a hydraulic pump to circulate high-pressure fluid. A rotary control valve regulates hydraulic pressure into the power cylinder to push the steering rack or pitman arm.

Characteristics: Delivers exceptionally communicative road feel and solid mechanical feedback, commonly found in older models and hardcore off-road 4x4s. The main drawbacks include parasitic engine load, complex plumbing, and the need for periodic power steering fluid replacement. 

Electro-Hydraulic Power Steering (EHPS - Electro-Hydraulic Power Steering): 

Working Principle: Instead of being driven directly by an engine belt, the hydraulic pump is powered by a dedicated electric motor. 

Characteristics: Combines hydraulic road feedback with electronically controlled flexibility, dynamically tailoring assist levels based on vehicle speed while reducing overall engine load. 

Electric Power Steering (EPS - Electric Power Steering): 

Working Principle: The prevailing industry standard today. It completely eliminates hydraulic fluid, applying assist torque directly via an electric motor mounted on the steering column or steering rack.

Characteristics: Highly energy-efficient (consumes power only during steering inputs), compact in design, and seamlessly integrates with Advanced Driver Assistance Systems (ADAS) such as Lane Keeping Assist and automated driving functions. 

How It Works: EPS as an Example

Sensing Input: When the driver turns the steering wheel, an integrated torque sensor instantly detects the magnitude and direction of the driver's steering input.

Data Processing: The EPS control unit (ECU) simultaneously evaluates signals from the vehicle speed sensor.

Low Speeds (e.g., Parking / Reversing): The ECU commands the motor to output high assist torque, delivering a feather-light steering feel for effortless manoeuvring. 

High Speeds (e.g., Highway Cruising): The ECU reduces power assistance or adds damping resistance to give the steering wheel a firmer, more weighted feel, preventing erratic directional changes caused by minor accidental inputs. 

Power Output: The electric motor drives the steering rack or steering column through a reduction gear mechanism to assist in steering the front wheels.

Common Faults and Troubleshooting Advice

Heavy Steering:

Hydraulic Systems: Inspect whether the power steering fluid level is low or if the drive belt is slipping. 

Electric Systems: Could be caused by a blown motor fuse, an assist control module fault, or a failed torque sensor; an OBD diagnostic scanner is required to retrieve the fault codes. 

Abnormal Noise / Whining: 

A whining noise in hydraulic systems typically indicates internal pressure loss in the power steering pump or aerated fluid (low fluid level).

In electric systems, abnormal motor noise is usually attributed to internal reduction gear wear. 

Steering Kickback or Failure to Self-Centre: Commonly caused by wheel alignment issues (such as incorrect caster angle) or mechanical binding in the steering rack; inspect the tie rod ends and ensure the steering rack is not over-tightened.

Routine Maintenance Tips 

Hydraulic Systems Require Regular Fluid Changes: It is recommended to flush and replace the power steering fluid every 40,000 to 60,000 km. Degraded fluid can deteriorate rubber seals, leading to a whining pump or steering rack leaks.

Avoid Dry Steering: Turning the steering wheel to full lock while stationary generates immense mechanical stress; always turn while the vehicle is creeping slightly to protect the electric motor or hydraulic pump. 

Inspect Rack Dust Boots: Regardless of system type, the rubber rack boots (gaiters) on both ends of the steering rack are essential to keep out dirt and moisture. Replace them immediately if any tears or cracks are found.